100+ Irish Surnames & Last Names: Meanings and Origins

Table of Content

Common Irish Surnames and Their Meanings How Irish Surnames Work: Ó, Mac, Mc, Ní and Nic Irish Surnames List A–Z: 100+ Names, Meanings and Gaelic Forms Irish Surnames A–C Irish Surnames D–H Irish Surnames I–M Irish Surnames N–R Irish Surnames S–Z Rare, Old and Uncommon Irish Surnames Irish Surnames by County and Region Munster Surnames Connacht Surnames Leinster Surnames Ulster Surnames How Irish Surnames Changed Over Time How to Trace Your Irish Surname and Family History Conclusion Frequently Asked Questions

Irish surnames carry layers of language, history, and family identity. Names such as Murphy, Kelly, O’Sullivan, Walsh, and O’Brien reflect Gaelic ancestry, regional roots, medieval dynasties, and centuries of spelling change and anglicization.

In this guide, you can explore 100+ Irish surnames and last names, including their Gaelic forms, meanings, origins, historic regional associations, and common variants. You’ll also find explanations of Irish surname prefixes such as Ó and Mac, rare and old family names, and practical ways to trace a surname through Irish family-history records.

Irish family explores Gaelic surname origins and ancestral records

Discover the roots and history behind Irish family names

Common Irish Surnames and Their Meanings

Many of Ireland’s best-known surnames grew from Gaelic patronymics, regional dynasties, or the arrival of Norman and Welsh families. Murphy, Kelly, Walsh, O’Sullivan, and O’Brien are among Ireland’s historically most numerous surnames, according to Robert E. Matheson’s Special Report on Surnames in Ireland, based on the 1890 Birth Indexes.

Here is a quick look at several common Irish surnames, their Irish forms, and what those names originally referred to.

Top 10 Irish family names with Gaelic forms, meanings, and regional ties

Top Irish last names reveal Gaelic roots and local heritage

Surname	Irish / Gaelic Form	Meaning or Origin	Historic Association
Murphy	Ó Murchadha	“Descendant of Murchadh.” The personal name Murchadh combines elements meaning “sea” and “battle,” giving the traditional interpretation “sea warrior.”	Several distinct Murphy families developed in Ireland rather than one single ancestral line.
Kelly	Ó Ceallaigh	“Descendant of Ceallach.” The personal name Ceallach has been interpreted in several ways, including “bright-headed” and later “frequenting churches,” so treat any single literal translation cautiously.	Strongly associated with the historic Uí Maine dynasty of Connacht, particularly Galway and Roscommon.
Walsh	Breathnach	A descriptive name meaning “Welsh person” or “Welshman,” associated with Welsh-speaking settlers who arrived in Ireland during the Anglo-Norman period.	Historically prominent in areas including Kilkenny, Mayo, and Waterford.
O’Sullivan	Ó Súileabháin / Ó Súilleabháin	“Descendant of Súileabhán.” The underlying personal name is traditionally connected with súil, meaning “eye”; interpretations of the full name vary, although “dark-eyed” is commonly cited.	Especially associated with Munster and the southwest of Ireland.
O’Brien	Ó Briain	“Descendant of Brian.” The surname is especially associated with the descendants of Brian Boru, High King of Ireland in the early 11th century.	Closely linked with the Dál gCais dynasty and Munster.
O’Connor	Ó Conchobhair	“Descendant of Conchobhar.” The deeper etymology of the personal name is less straightforward, so the patronymic meaning is more reliable than a simplified literal translation.	Several important O’Connor families developed in Ireland, including the royal dynasty of Connacht.
Ryan	Ó Riain / Ó Riaghain	“Descendant of Riaghan.” The personal name may be related to rí, the Irish word for “king,” although Ryan also developed from other Irish surname forms.	Particularly associated with Munster, though the surname is now widespread.
O’Neill	Ó Néill	“Descendant of Niall.” The surname is historically connected with the powerful Uí Néill dynasties, traditionally linked to Niall of the Nine Hostages.	Most strongly associated with Ulster, especially Tyrone.

These meanings offer useful clues to how Irish surnames developed. Still, don't treat them as fixed definitions for every family line, since spelling, regional history, and anglicization can vary.

For a broader lookup, explore the A–Z list below for 100+ Irish surnames with their Gaelic forms, meanings, historic associations, and common variants.

How Irish Surnames Work: Ó, Mac, Mc, Ní and Nic

Many traditional Irish surnames use prefixes that originally described descent. Ó generally indicates descent from an ancestor, while Mac means “son of.” Irish-language surnames may also use Ní or Nic for women, while anglicization produced familiar forms such as O’ and Mc.

Form	Basic Meaning / Function	Example
Ó / O’	Descendant of an ancestor	Ó Briain → O’Brien
Mac / Mc	Son of; Mc is an anglicized form of Mac	Mac Cárthaigh → MacCarthy / McCarthy
Mag	A grammatical variant of Mac in certain surnames	Mag Uidhir → Maguire
Ní	Female Irish-language form used with Ó-based surnames	Ní Cheallaigh
Nic	Female Irish-language form used with Mac-based surnames	Nic Mhathúna
Fitz	Norman patronymic meaning “son of”	FitzGerald

What Does Ó or O’ Mean in Irish Surnames?

Ó marks descent from an ancestor and is usually rendered as O’ in English. For example, Ó Briain became O’Brien and Ó Néill became O’Neill. Some families later dropped the prefix during anglicization, which is why related surname forms may appear both with and without O’.

What Do Mac and Mc Mean?

Mac means “son of,” while Mc is an anglicized abbreviated spelling of the same prefix. Names such as Mac Cárthaigh became MacCarthy or McCarthy. Mag is a grammatical form related to Mac and appears in surnames such as Mag Uidhir, the Irish form behind Maguire.

What Are Ní and Nic in Irish Surnames?

In Irish-language surnames, women may use Ní with names based on Ó and Nic with names based on Mac:

Ó Ceallaigh → Ní Cheallaigh
Mac Mathúna → Nic Mhathúna

These forms come from traditional Irish naming grammar, and the following surname may also change spelling. Anglicized English surnames generally do not change by gender.

What Does Fitz Mean in Irish Surnames?

Fitz comes from the Anglo-Norman naming tradition rather than Gaelic Irish. Derived from Old French fils, meaning “son,” it appears in names such as FitzGerald, FitzMaurice, and FitzSimons and became established in Ireland after the Anglo-Norman settlement.

Knowing these forms makes it easier to recognize how modern Irish surnames relate to their earlier Gaelic or Norman origins.

Irish Surnames List A–Z: 100+ Names, Meanings and Gaelic Forms

Use this A–Z directory to look up 100+ Irish surnames and last names, including their Gaelic forms, meanings or origins, and historic regional associations. Use Ctrl + F on Windows or ⌘ + F on Mac to find a specific name, and try common O’/Ó or Mac/Mc variants if the spelling you expect does not appear.

Note: Surname meanings are simplified for quick reference, and some names have more than one possible origin or interpretation. Regional associations show historic concentrations, not a guaranteed place of origin for every family. Historical distribution and surname forms have been cross-checked against Robert E. Matheson’s Special Report on Surnames in Ireland, and Irish surname reference works.

Irish Surnames A–C

Surname / Common Variant	Irish / Gaelic Form	Meaning or Origin	Historic Association
Barry	de Barra	Norman surname derived from the de Barra family	Cork; Norman-Irish Munster
Bell	—	English or Scottish surname later established in Ireland	Mainly Ulster
Boland	Ó Beólláin	Descendant of Beóllán	Offaly, Clare, Mayo
Boyle / O’Boyle	Ó Baoill / Ó Baoighill	Descendant of Baoill	Donegal
Boylan	Ó Baoighealláin	Descendant of Baoigheallán	Meath, Cavan, Armagh
Brady	Ó Brádaigh	Descendant of Brádach; the underlying name has several interpretations	Cavan and surrounding Ulster
Brennan	Ó Braonáin / Ó Branáin	Descendant of Braonán or Branán	Kilkenny, Roscommon, Sligo
Breen	Ó Braoin	Descendant of Braon	Clare, Limerick
Burke / Bourke	de Burgh	Norman surname from the de Burgh family	Galway, Mayo
Burns	Various origins	Usually Scottish in origin; some families became established in Ireland	Mainly Ulster
Butler	Butler	Occupational or hereditary title associated with a household steward	Kilkenny, Tipperary
Byrne / O’Byrne	Ó Broin	Descendant of Bran; Bran is traditionally associated with the raven	Wicklow and Leinster
Cahill	Ó Cathail	Descendant of Cathal	Tipperary, Clare
Campbell	Caimbeul	Scottish Gaelic surname later established in Ireland	Ulster
Canavan	Ó Ceanndubháin	Descendant of Ceanndubhán; traditionally linked with a dark-haired ancestor	Galway, Mayo
Carroll / O’Carroll	Ó Cearbhaill	Descendant of Cearbhall	Offaly, Louth, Tipperary
Casey / O’Casey	Ó Cathasaigh	Descendant of Cathasach	Dublin, Cork and other branches
Collins	Ó Coileáin	Descendant of Coileán, traditionally interpreted as “young hound”	Cork
Colgan	Ó Colgáin	Descendant of Colgán	Galway, Mayo
Connolly	Ó Conghalaigh	Descendant of Conghalach	Monaghan, Donegal, Galway
Cosgrave	Ó Coscraigh	Descendant of Coscrach, commonly interpreted as “victorious”	Laois, Westmeath
Coughlan / Coghlan	Mac Cochláin	Son or descendant of Cochlán	Offaly
Crean	Ó Croidheagáin	Descendant of Croidheagán	Kerry
Cullen	Ó Cuileáin	Descendant of Cuileán, “young hound”	Kilkenny, Wicklow

Byrne Irish surname with Gaelic Ó Broin roots, meaning, and Wicklow heritage

Byrne family name traces Gaelic roots to County Wicklow

Irish Surnames D–H

Surname / Common Variant	Irish / Gaelic Form	Meaning or Origin	Historic Association
Dempsey	Ó Díomasaigh	Descendant of Díomasach; traditionally associated with pride or dignity	Laois
Doherty / O’Doherty	Ó Dochartaigh	Descendant of Dochartach	Donegal and northwest Ulster
Donnelly	Ó Donnghaile	Descendant of Donnghal	Tyrone and Ulster
Donohoe / Donoghue	Ó Donnchadha	Descendant of Donnchadh	Kerry, Cork and other branches
Donovan	Ó Donnabháin	Descendant of Donnabhán	Cork
Doyle	Ó Dubhghaill	Descendant of Dubhghall, traditionally interpreted as “dark foreigner”	Wicklow and Leinster
Duffy	Ó Dubhthaigh	Descendant of Dubthach	Donegal, Monaghan
Dunne / Dunn	Ó Duinn	Descendant of Donn, associated with brown or dark coloring	Laois, Offaly
Dwyer / O’Dwyer	Ó Duibhir	Descendant of Duibhir	Tipperary
Egan	Mac Aodhagáin	Son or descendant of Aodhagán	Offaly, Tipperary
Fagan	Ó Faodhagáin	Descendant of Faodhagán	Meath, Westmeath
Farrell / O’Farrell	Ó Fearghail	Descendant of Fearghal	Longford
Finnegan	Ó Fionnagáin	Descendant of Fionnagán, traditionally linked with fair coloring	Monaghan and parts of Connacht
Fitzgerald	Mac Gearailt; Fitzgerald	“Son of Gerald,” from Norman French fitz	Kildare, Kerry
Fitzmaurice	Mac Muiris; Fitzmaurice	“Son of Maurice”	Kerry
Fitzpatrick	Mac Giolla Phádraig	Son of the devotee or servant of St. Patrick	Laois / historic Osraige
Flanagan	Ó Flannagáin	Descendant of Flannagán; connected with flann, “red” or “ruddy”	Roscommon, Fermanagh
Flannery	Ó Flannghaile	Descendant of Flannghal	Mayo and Connacht
Flynn / O’Flynn	Ó Floinn	Descendant of Flann, “ruddy” or “red”	Cork, Clare, Roscommon
Foley	Ó Foghladha	Descendant of Foghlaidh	Kerry and Munster
Gaffney	Ó Gamhna	Descendant of Gamhain; traditionally associated with “calf”	Cavan, Monaghan
Gallagher	Ó Gallchobhair	Descendant of Gallchobhar	Donegal
Geoghegan	Mag Eochagáin	Descendant of Eochagán	Westmeath
Gorman	Mac Gormáin / Ó Gormáin	Descendant of Gormán; more than one family line existed	Clare, Wexford and other regions
Hayes	Ó hAodha	Descendant of Aodh, a personal name associated with fire	Cork, Limerick
Healy	Ó hÉalaighthe	Descendant of Éaladhach	Cork, Sligo
Hegarty	Ó hÉigeartaigh	Descendant of Éigeartach	Donegal
Hennessy	Ó hAonghusa	Descendant of Aonghus	Cork
Higgins	Ó hUiginn	Descendant of Uiginn	Mayo, Sligo
Hogan	Ó hÓgáin	Descendant of Ógán, connected with “young”	Tipperary, Kilkenny
Hughes	Often Ó hAodha in Irish families	Frequently an anglicized form connected with Aodh; the surname also has Welsh origins	Especially Ulster

Gallagher Gaelic family name Ó Gallchobhair, meaning foreign helper with Donegal roots

Gallagher ancestry reveals Ó Gallchobhair roots in Donegal

Irish Surnames I–M

Surname / Common Variant	Irish / Gaelic Form	Meaning or Origin	Historic Association
Kane / O’Kane	Ó Catháin	Descendant of Cathán	Derry, Tyrone
Kavanagh	Caomhánach	Dynastic surname connected with Domhnall Caomhánach	Carlow, Wexford
Keane	Often Ó Catháin	One of several anglicized forms associated with Ó Catháin and other Irish names	Clare, Galway and elsewhere
Kearney	Ó Catharnaigh	Descendant of Catharnach	Offaly, Tipperary
Keating	Céitinn	Norman surname established in medieval Ireland	Kilkenny, Tipperary
Keenan	Ó Cianáin	Descendant of Cianán	Monaghan, Fermanagh
Kelly / O’Kelly / Kelley	Ó Ceallaigh	Descendant of Ceallach; several interpretations exist for the personal name	Galway, Roscommon and several other branches
Kennedy	Ó Cinnéide	Descendant of Cinnéidigh / Cinnéide	Tipperary and Munster
Lynch	Ó Loingsigh; also Norman Lynch families	Gaelic and Norman-Irish origins exist	Galway, Clare and elsewhere
Madden	Ó Madadháin	Descendant of Madadhán	Galway
Magee / McGee	Mag Aodha / Mac Aodha	Son or descendant of Aodh	Donegal, Down, Tyrone
Maguire	Mag Uidhir	Descendant of Odhar / Uidhir	Fermanagh
Maher / Meagher	Ó Meachair	Descendant of Meachar	Tipperary
Martin	Mac Giolla Mhártain in some Irish families	Devotee or servant of St. Martin; other Norman and English origins also exist	Galway and elsewhere
McCarthy / MacCarthy	Mac Cárthaigh	Son or descendant of Cárthach	Cork, Kerry and Munster
McCloskey	Mac Bhloscaidh	Son or descendant of Bloscadh	Derry
McDermott / MacDermot	Mac Diarmada	Son or descendant of Diarmaid	Roscommon
McGovern	Mag Samhradháin	Descendant of Samhradhán	Cavan
McGrath / MacGrath	Mac Craith	Son or descendant of Craith	Waterford, Clare, Tipperary
McKeon	Mac Eoin	Son of Eoin, the Irish form of John	Roscommon, Sligo and Midlands
McMahon / MacMahon	Mac Mathghamhna	Son or descendant of Mathghamhain, traditionally associated with the bear	Clare, Monaghan
McManus	Mac Maghnuis	Son of Magnus	Fermanagh
Molloy	Ó Maolmhuaidh	Descendant of Maolmhuaidh	Offaly, Westmeath
Moloney / Maloney	Ó Maoldomhnaigh	Descendant of Maoldomhnaigh	Clare and Munster
Moore / O’More	Ó Mórdha in one important Irish line	Descendant of Mórdha; Moore also has English and Scottish origins	Laois and elsewhere
Moran	Ó Móráin	Descendant of Mórán	Galway, Roscommon
Mullen	Ó Maoláin	Descendant of Maolán	Ulster, Connacht
Mulligan	Ó Maolagáin	Descendant of Maolagán	Donegal, Westmeath
Muldoon	Ó Maoldúin	Descendant of Maoldúin	Fermanagh
Murphy	Ó Murchadha	Descendant of Murchadh; the personal name is traditionally interpreted as “sea warrior”	Multiple families, especially Leinster and Munster
Murray	Ó Muireadhaigh in some Irish lines	Descendant of Muireadhach; Murray also has Scottish origins	Donegal, Roscommon and elsewhere

Murphy family name from Ó Murchadha, meaning sea warrior in Gaelic tradition

Murphy’s Gaelic roots evoke the bold meaning of sea warrior

Irish Surnames N–R

Surname / Common Variant	Irish / Gaelic Form	Meaning or Origin	Historic Association
Nolan	Ó Nualláin	Descendant of Nuallán	Carlow, Kilkenny
O’Brien / Brien	Ó Briain	Descendant of Brian; famously associated with the descendants of Brian Boru	Clare and Munster
O’Carroll / Carroll	Ó Cearbhaill	Descendant of Cearbhall	Offaly, Tipperary, Louth
O’Casey / Casey	Ó Cathasaigh	Descendant of Cathasach	Dublin, Cork and other branches
O’Clery / O’Cleary / Cleary	Ó Cléirigh	Descendant of Cléireach / the cleric or scholar	Donegal; earlier associations in Connacht
O’Connell	Ó Conaill	Descendant of Conall	Kerry
O’Connor / Connor	Ó Conchobhair	Descendant of Conchobhar	Connacht and several independent branches
O’Donnell	Ó Domhnaill	Descendant of Domhnall	Donegal
O’Donoghue / Donoghue	Ó Donnchadha	Descendant of Donnchadh	Kerry, Cork
O’Driscoll / Driscoll	Ó hEidirsceoil	Descendant of Eidirsceol	Cork
O’Farrell / Farrell	Ó Fearghail	Descendant of Fearghal	Longford
O’Hara	Ó hEaghra	Descendant of Eaghra	Sligo, Mayo
O’Keeffe / Keeffe	Ó Caoimh	Descendant of Caomh; traditionally associated with gentleness or nobility	Cork
O’Leary / Leary	Ó Laoghaire	Descendant of Laoghaire	Cork
O’Mahony / Mahony	Ó Mathghamhna	Descendant of Mathghamhain	Cork, Kerry
O’Neill / Neill	Ó Néill	Descendant of Niall	Tyrone, Armagh and wider Ulster
O’Reilly / Reilly	Ó Raghallaigh	Descendant of Raghallach	Cavan
O’Rourke / Rourke	Ó Ruairc	Descendant of Ruairc	Leitrim and Breifne
O’Shea / Shea	Ó Séaghdha	Descendant of Séaghdha; the personal name has several traditional interpretations	Kerry
O’Sullivan / Sullivan	Ó Súileabháin / Ó Súilleabháin	Descendant of Súileabhán; the name is traditionally linked with súil, “eye,” but its full etymology is debated	Cork, Kerry
Phelan / Whelan	Ó Faoláin	Descendant of Faolán, “little wolf”	Kilkenny, Waterford
Power	de Paor	Norman surname established in Ireland after the Anglo-Norman settlement	Waterford
Quinn / Quin	Ó Cuinn	Descendant of Conn	Tyrone, Clare and several other branches
Regan / Reagan	Ó Riagáin	Descendant of Riagán	Cork, Tipperary and other regions
Roche	de Róiste	Norman-Irish surname, traditionally associated with the Norman de la Roche name	Cork, Wexford
Ryan	Ó Riain / Ó Maoilriain	More than one Irish family origin is associated with the modern surname Ryan	Tipperary, Limerick and Munster

O’Neill name from Gaelic Ó Néill, meaning descendant of Niall with Ulster heritage

O’Neill ancestry reflects deep Ó Néill roots across Ulster

Irish Surnames S–Z

Surname / Common Variant	Irish / Gaelic Form	Meaning or Origin	Historic Association
Scully	Ó Scolaidhe	Descendant of Scolaidhe, traditionally connected with “scholar”	Tipperary
Sheehan	Ó Síodhacháin	Descendant of Síodhachán, associated with peace	Cork, Kerry
Sheridan	Ó Sirideáin	Descendant of Sirideán	Cavan, Longford
Smith / Smyth	Mac Gabhann in some Irish families	Occupational surname meaning “smith”; not every Irish Smith descends from Mac Gabhann	Found throughout Ireland
Sweeney / MacSweeney	Mac Suibhne	Son or descendant of Suibhne	Donegal
Tiernan	Ó Tiarnáin	Descendant of Tiarnán	Cavan, Leitrim
Tierney	Ó Tiarnaigh	Descendant of Tiarnaigh	Galway, Roscommon and other branches
Tracy / Treacy	Ó Treasaigh	Descendant of Treasach, traditionally associated with fighting or strength	Limerick, Tipperary, Wexford
Ward	Mac an Bhaird	“Son of the bard”	Donegal, Galway and other branches
Walsh / Walshe	Breathnach	“Welsh person,” reflecting Welsh settlement in medieval Ireland	Kilkenny, Wexford and other regions

Irish surnames often appear in several spellings because of anglicization and historical record-keeping. Use the Gaelic form, known variants, and regional association as starting points when comparing a surname with family records.

The next section looks more closely at rare, uncommon, and older Irish surnames.

Rare, Old and Uncommon Irish Surnames

Beyond familiar names such as Murphy, Kelly, and O’Brien, Ireland has many older or less familiar surnames tied to particular regions, learned families, and medieval dynasties. Some survive in small numbers or under altered English spellings. In contrast, others are notable because their recorded histories reach back to the early development of hereditary surnames in Ireland.

Here, rare and uncommon are used descriptively rather than as strict population rankings. A surname may be uncommon nationally while remaining strongly associated with one county or region.

Rare and Uncommon Irish Surnames

Many less familiar Irish surnames preserve especially distinctive links to local territories, professions, or hereditary learned families. Their modern forms can also differ substantially from the original Irish name because of centuries of anglicization.

Surname	Irish / Gaelic Form	Meaning or Origin	Why It Is Notable
Davoren / Davern	Ó Dábhoireann	Descendant of Dubhdábhoireann	A learned legal family of Thomond associated with a historic Brehon law school in County Clare.
Mulconry / Conry	Ó Maolchonaire	Descendant of Maolchonaire, “follower of Conaire”	A celebrated hereditary family of poets and chroniclers connected with the kings of Connacht.
O’Shaughnessy / Shaughnessy	Ó Seachnasaigh	Descendant of Seachnasach	Historically associated with the Uí Fiachrach Aidhne and the Gort area of County Galway.
O’Dea / Dea	Ó Deaghaidh	Descendant of Deaghadh	A Dalcassian surname historically associated with Thomond and County Clare, with another family recorded in Tipperary.
O’Clery / O’Cleary / Cleary	Ó Cléirigh	Descendant of Cléireach, associated with “clerk” or “cleric”	One of Ireland’s great learned families; later O’Clery scholars became closely associated with Irish historical writing.
O’Naughton / Naughton	Ó Neachtain	Descendant of Neachtan	An old Connacht surname with historic associations in the west of Ireland.
MacMahon / McMahon	Mac Mathghamhna	Son or descendant of Mathghamhain	Two major historical families carried the name, one in Thomond and another in Oriel, showing that the same surname could develop through distinct lineages.
O’Mahony / Mahony	Ó Mathghamhna	Descendant of Mathghamhain	An old Cork family whose medieval territory lay in southwest Munster.

O’Shaughnessy Gaelic name Ó Seachnasaigh with scholarly roots in County Clare

O’Shaughnessy preserves rare Gaelic heritage from Clare

These examples also show why an uncommon spelling should not automatically be treated as a separate lineage. Irish surnames were frequently translated, shortened, phonetically recorded, or replaced by English-looking forms, so one Gaelic surname can produce several modern variants.

Some of the Oldest Irish Surnames

Hereditary surnames began developing in Ireland from roughly the 10th century onward, particularly through names formed with Ó and later Mac. Ireland was therefore an early adopter of hereditary family names, although these naming practices developed gradually rather than appearing everywhere at once.

Several well-known surnames can be traced to powerful families or named ancestors from this early medieval period:

Surname	Irish Form	Early Historical Connection
O’Clery / Cleary	Ó Cléirigh	Connected with the descendants of Cléireach, an ancestor said to have flourished in the 9th century; the surname is associated with a record from 916.
O’Neill	Ó Néill	The major Ulster line took its surname from Niall Glúndubh; Woulfe identifies Domhnall Ó Néill, mentioned in 943, as the first recorded bearer of the surname.
O’Connor	Ó Conchobhair	Several independent families bore the name; the Connacht dynasty traced its surname to Conchobhar, a 10th-century king of Connacht.
O’Brien	Ó Briain	Means “descendant of Brian” and is historically tied to the descendants of Brian Boru, who died in 1014.
O’Byrne / Byrne	Ó Broin	The Leinster family traced its name to Bran, son of Máel Mórda, whose death is recorded in the 11th century.
O’Mahony / Mahony	Ó Mathghamhna	The Cork family traced descent from Mathghamhain, recorded as dying in 1014.

So, what is the oldest recorded Irish surname?
O’Clery (Ó Cléirigh) is commonly cited as the earliest known hereditary Irish surname, with a family member recorded in 916 AD. Some modern sources go further and describe it as a possible candidate for the earliest recorded hereditary surname in Europe, but that broader European claim is best treated cautiously rather than as settled fact.

“Old,” however, does not necessarily mean that every modern bearer descends from one continuous family line. Independent branches, spelling changes, migration, and anglicization can all complicate the connection between a medieval surname and a present-day family.

Irish Surnames by County and Region

Irish surnames often have strong historic links to particular counties and provinces. Still, a surname alone cannot prove where one modern family originated. Migration, marriage, anglicization, and unrelated families with the same surname mean regional associations are clues, not guarantees.

The examples below are based mainly on surname distribution recorded in Ireland’s 1890 Birth Indexes, compiled by Registrar-General Robert E. Matheson. The report records surnames by province and notes the counties in which they were principally found, making it useful for identifying historical concentrations rather than present-day population patterns.

Munster Surnames

Munster—covering counties such as Cork, Kerry, Clare, Limerick, Tipperary, and Waterford—has especially strong historic associations with names including O’Sullivan, McCarthy, O’Brien, Ryan, and Power.

Surname	Historic Association	Where It Was Especially Prominent
O’Sullivan / Sullivan	One of the strongest surname traditions of southwest Ireland	Cork and Kerry
McCarthy / MacCarthy	Major Gaelic dynasty of Munster	Cork and Kerry
O’Brien	Closely associated with the Dál gCais and descendants of Brian Boru	Clare and wider Munster
Ryan	Particularly strong in central and eastern Munster	Tipperary and Limerick
McMahon	Important Dalcassian family in the region	Clare
Power	Norman-Irish surname with a long regional presence	Waterford
O’Connell	Strong historic concentration in southwest Ireland	Kerry, Cork, and Limerick
Mahony / O’Mahony	Old Munster surname with a particularly strong Cork presence	Cork and Kerry

O’Sullivan Gaelic family name Ó Súilleabháin with deep Cork and Kerry roots

O’Sullivan heritage highlights historic roots in Cork and Kerry

Connacht Surnames

Connacht includes Galway, Mayo, Roscommon, Sligo, and Leitrim. Historic surname patterns here include several major Gaelic families as well as names that remain closely associated with the west of Ireland.

Surname	Historic Association	Where It Was Especially Prominent
Kelly / O’Kelly	Associated with several Irish families, including the Uí Maine	Galway and Roscommon
Burke / Bourke	Norman-Irish family deeply established in Connacht	Galway and Mayo
Walsh	Numerous western Irish branches developed over time	Mayo and Galway
Moran	Longstanding western surname found across several counties	Mayo, Galway, and Roscommon
McDermott / MacDermot	Historically connected with the kingdom of Moylurg	Roscommon
O’Hara	Old Connacht surname	Sligo
Joyce	Strongly associated with western Galway and Mayo	Galway and Mayo
Flaherty / O’Flaherty	Major historic Galway family	Galway

Leinster Surnames

Leinster covers eastern and southeastern Ireland, including Dublin, Wicklow, Wexford, Carlow, Kildare, Kilkenny, Laois, Offaly, Meath, Westmeath, Longford, and Louth. Its surname landscape reflects Gaelic families, Norman settlement, and centuries of movement toward Dublin.

Surname	Historic Association	Where It Was Especially Prominent
Byrne / O’Byrne	Major Gaelic family of Leinster	Wicklow, Dublin
Kavanagh	Descended from a branch of the MacMurrough dynasty	Carlow and Wexford
Doyle	Strong historic presence in eastern Ireland	Wicklow and Wexford
Nolan	Long associated with southeast Leinster	Carlow
Brennan	Important historic surname in the southeast	Kilkenny
Dunne	Strongly associated with the Irish midlands	Laois
O’Farrell / Farrell	Historic ruling family of Annaly	Longford
O’Reilly / Reilly	Strong in the north Midlands as well as neighboring Ulster areas	Meath and nearby counties

Ulster Surnames

Ulster has a particularly mixed surname landscape shaped by Gaelic Irish families, Scottish migration, and the Plantation of Ulster. Traditional Gaelic surnames such as O’Neill, O’Donnell, Gallagher, Doherty, and Maguire appear alongside Scottish and English names that became deeply established in the province.

Surname	Historic Association	Where It Was Especially Prominent
O’Neill	One of the most powerful Gaelic dynasties of Ulster	Tyrone and Armagh
O’Donnell	Major Gaelic ruling family of northwest Ulster	Donegal
Gallagher	Longstanding Donegal surname	Donegal
Doherty / O’Doherty	Historic Inishowen family	Donegal
Maguire	Ruling family historically associated with Fermanagh	Fermanagh
Quinn	Strong historic concentration in central Ulster	Tyrone
Duffy	Particularly numerous in parts of Ulster	Monaghan
Campbell	Scottish Gaelic surname established in Ulster	Antrim and Armagh

Regional surname patterns are most useful when combined with other evidence. If a family tradition points to a county, compare that clue with the surname’s Gaelic form, known spelling variants, and records for a specific ancestor rather than assuming everyone with the same surname comes from one place.

How Irish Surnames Changed Over Time

Irish surnames changed through centuries of language shift, migration, and record-keeping. A single family name may therefore appear in several forms, such as Ó Briain / O’Brien, Mac Cárthaigh / MacCarthy / McCarthy, or Ó Súilleabháin / O’Sullivan / Sullivan.

Timeline showing Irish family names evolving through Gaelic, Norman, and Anglicized forms

Centuries of change shaped Irish names from Gaelic to global

The Rise of Hereditary Irish Surnames

Hereditary surnames became increasingly established in Ireland from around the 10th and 11th centuries. Earlier names often identified a person through a father or ancestor, but forms using Ó and Mac gradually became inherited family names.

This is why surnames such as Ó Néill, Ó Briain, Ó Conchobhair, and Mac Cárthaigh preserve links to medieval ancestors or dynastic families. However, the same modern surname can sometimes come from more than one historical line, so a surname alone does not prove shared ancestry.

Norman and Norman-Welsh Influence

The Anglo-Norman settlement from the late 12th century onward introduced another layer of surnames to Ireland. Families with names such as Burke, Barry, Fitzgerald, FitzMaurice, Butler, Power, Roche, and Walsh became established across different regions.

The prefix Fitz, seen in names such as Fitzgerald and FitzMaurice, comes from Norman French and means “son of.” Walsh, meanwhile, developed from a term referring to a Welsh person and reflects Welsh settlement in medieval Ireland.

Over time, many Norman families became deeply integrated into Irish society, making the distinction between “Gaelic” and “Norman” surnames less clear-cut than it may first appear.

Anglicization and Spelling Variants

Anglicization created some of the biggest changes in Irish surnames. Irish-language names were often rewritten according to English spelling, pronunciation, or administrative conventions.

For example:

Ó Briain → O’Brien
Mac Cárthaigh → MacCarthy / McCarthy
Ó Donnchadha → O’Donoghue / Donoghue
Ó Faoláin → Phelan / Whelan
Ó Súilleabháin → O’Sullivan / Sullivan

Families sometimes also dropped O’ or Mac, while clerks and record keepers could spell the same surname differently from one document to another.

For family-history research, these variations matter. Searching only one modern spelling can cause you to miss older records.

Irish Surnames in America and the Diaspora

Irish migration carried surnames to Britain, North America, Australia, New Zealand, and other parts of the diaspora, where spelling continued to evolve.

Prefixes could disappear, Mac and Mc might alternate, and unfamiliar spellings were sometimes simplified. A family recorded as O’Sullivan in Ireland, for example, might later appear as Sullivan. At the same time, related records may list both MacCarthy and McCarthy.

When tracing an Irish surname, it is therefore useful to search several forms of the name and compare them with dates, locations, relatives, and the original Gaelic form rather than relying on one exact spelling.

How to Trace Your Irish Surname and Family History

An Irish surname can offer useful clues, but reliable family-history research should combine the name with Gaelic forms, spelling variants, locations, dates, and records tied to known relatives.

Irish genealogy research with family records, maps, and Gaelic name sources

Trace Irish family roots through records, maps, and genealogy

1. Find the Original Irish or Gaelic Form

Start with the Irish-language form of the surname, such as Ó Briain for O’Brien or Mac Cárthaigh for McCarthy. Older records may use a form that looks very different from the modern English spelling.

2. Record Known Spelling Variants

Irish surnames often appear in several forms, including O’Reilly / Reilly, MacCarthy / McCarthy, and O’Sullivan / Sullivan. Searching multiple spellings can uncover records you might otherwise miss.

3. Check Historic County Associations

Look for counties or regions historically linked to the surname, but treat them as clues rather than proof. The same surname may belong to more than one family line, and families often moved over time.

4. Search Irish Genealogy Records

Use records tied to specific people rather than surname history alone. Useful sources include IrishGenealogy.ie, the National Archives of Ireland, parish registers, census records, and Griffith’s Valuation.

Compare names with dates, places, occupations, and relatives to confirm that records belong to the same family.

5. Verify the Family Branch

Do not assume that everyone with the same surname belongs to one clan or lineage. The safest approach is to begin with the most recent known ancestor and work backward one generation at a time.

Research tip: A surname meaning or county association can guide your search, but documentary records are what establish the actual family connection.

Conclusion

Irish surnames can reveal valuable clues about language, regional roots, spelling changes, and family history. Their Gaelic forms and variants often help explain how a name developed over time.

If you are researching your own surname, start with the Gaelic form, known spelling variants, and confirmed family locations, then work backward through historical records to verify the actual family line.

Frequently Asked Questions

Are Irish surnames the same as Gaelic surnames?

Not always. Many Irish surnames have Gaelic origins, such as O’Brien (Ó Briain) and McCarthy (Mac Cárthaigh). Still, Ireland also has Norman, Welsh, English, Scottish, and other surnames. Centuries of settlement and language change have made Irish surname history more diverse than a purely Gaelic naming tradition.

Can two unrelated families have the same Irish surname?

Yes. The same surname can develop in separate family lines, and later anglicization sometimes caused different Gaelic names to end up with similar English spellings. A shared surname is therefore a useful research clue, but it does not prove a common ancestor on its own.

Why did some Irish families drop the O’ from their surnames?

Some dropped O' as Irish surnames were anglicized and adapted to English-language records. Usage also varied by family and generation, and some descendants later restored the prefix. As a result, historical and modern records may show forms such as O’Sullivan/Sullivan or O’Reilly/Reilly.

What is the difference between an Irish surname and an Irish clan name?

An Irish surname identifies a family name, while a historical clan or kin group could include multiple related branches and surnames. A modern surname may have associations with a particular dynasty or territory, but the name alone is not enough to establish membership in a specific historical clan.

Can an Irish surname tell you whether your family is from Ireland?

It can suggest Irish ancestry, but it is not proof on its own. Many Irish surnames spread through Britain, North America, Australia, New Zealand, and elsewhere, while some surnames found in Ireland also have Scottish, English, Norman, or Welsh origins. Family records and known ancestral locations provide stronger evidence.

Aimee Li

An author dedicated to exploring the rich history, vibrant culture,... of the Scottish clans. As an avid historian and fashion enthusiast, I have always been fascinated by Scotland's heritage and the timeless elegance of its traditional attire. Join me on this journey through the highlands and lowlands, as we delve into the heart of Scottish legacy together.