surnames.ie

Irish surname · 7th most common in 1911

O'Brien

Also spelt Brien

O'Brien comes from the Irish Ó Briain, 'descendant of Brian', and traces its descent from Brian Boru, the Munster king killed at Clontarf in 1014. His descendants ruled Thomond, centred on County Clare, and the name later spread throughout Ireland.

Irish Ó BriainIrish Mac Bhriain
1901 census
31,060
#7 · 70 per 10,000
1911 census
31,022
#7 · 71 per 10,000
1926 census
30,138
#6 · 102 per 10,000
Most numerous
Cork
Highest share: Tipperary

Language & meaning

Meaning & Irish forms

Gaelic Gaelic Irish: a royal Dál gCais (Dalcassian) family of Thomond, descended from Brian Boru.[1][2]

Ó Briain
“descendant of Brian”[1][2][3]
Classical Irish Ua Briain; a daughter is Ní Bhriain and a wife Bean Uí Bhriain.
Mac Bhriain
“son of Brian”[4]
A separate patronymic, anglicised MacBrien and MacBryan.

The name is built on the personal name Brian, usually explained as “uncertain; possibly from an Old Celtic word for 'high' or 'noble'”. Woulfe gives no meaning for the name. The etymology on Wikipedia is offered only as a possibility.[5]

Pronunciation

O'Brien: oh-BRY-en (Woulfe notes it was once said 'O'Breen')

Ó Briain: oh BREE-in /oː ˈbʲɾʲiənʲ/[2]

Place

Where the O'Briens lived

How common the name was in each county, as a share of the population, in the three surviving full censuses of Ireland. Use the buttons to compare years.

Donegal: 25.4 per 10,000 (428 people) Waterford: 182.1 per 10,000 (1,499 people) Dublin: 86.8 per 10,000 (4,169 people) Kilkenny: 72.7 per 10,000 (546 people) Carlow: 108.4 per 10,000 (394 people) Limerick: 188.7 per 10,000 (2,705 people) Louth: 43 per 10,000 (271 people) Tipperary: 211.7 per 10,000 (3,231 people) Roscommon: 31.8 per 10,000 (299 people) Meath: 113.8 per 10,000 (742 people) Wicklow: 149.4 per 10,000 (909 people) Cavan: 33.7 per 10,000 (308 people) Cork: 151.5 per 10,000 (5,957 people) Clare: 160.3 per 10,000 (1,674 people) Galway: 51.2 per 10,000 (933 people) Mayo: 44.6 per 10,000 (857 people) Sligo: 22.1 per 10,000 (175 people) Leitrim: 37.1 per 10,000 (234 people) Offaly: 78.7 per 10,000 (448 people) Laois: 47.9 per 10,000 (262 people) Kildare: 88.7 per 10,000 (593 people) Kerry: 81.3 per 10,000 (1,300 people) Monaghan: 29.4 per 10,000 (210 people) Wexford: 135.7 per 10,000 (1,390 people) Longford: 15.1 per 10,000 (66 people) Westmeath: 49.2 per 10,000 (296 people) Tyrone: 21.9 per 10,000 (313 people) Antrim: 6.1 per 10,000 (293 people) Armagh: 6.4 per 10,000 (76 people) Fermanagh: 22.9 per 10,000 (139 people) Londonderry: 11.7 per 10,000 (163 people) Down: 4.6 per 10,000 (142 people)
fewerup to 218 per 10,000

Share of each county's census population. 1926 covers the 26 counties of the Irish Free State only.

Highest concentration · 1911

Tipperary

212 per 10,000

3,231 O'Briens · 3× the national share

Highest share, 1911

  1. Tipperary 212
  2. Limerick 189
  3. Waterford 182
  4. Clare 160
  5. Cork 152
  6. Wicklow 149
  7. Wexford 136
  8. Meath 114

Per 10,000 residents. A concentration index above 1 means the name was commoner there than nationally.

County figures as a table
County190119111926Per 10k 1901Per 10k 1911Per 10k 1926
Antrim306293—76—
Armagh7576—66—
Carlow384394392103108114
Cavan296308290303435
Clare1,8451,6741,531164160161
Cork6,2855,9575,905157152162
Donegal393428458232530
Down191142—75—
Dublin3,6274,1694,890838798
Fermanagh126139—1923—
Galway944933950495156
Kerry1,2991,3001,316788188
Kildare5095935978389103
Kilkenny450546529607375
Laois203262225364844
Leitrim260234236373742
Limerick2,8262,7052,661192189191
Londonderry177163—1212—
Longford776666171517
Louth242271307374349
Mayo843857775434545
Meath746742720106114115
Monaghan180210218242934
Offaly453448464757989
Roscommon334299292333235
Sligo183175172232224
Tipperary3,4213,2313,051214212218
Tyrone304313—2022—
Waterford1,6141,4991,440185182185
Westmeath303296313494955
Wexford1,3991,3901,434135136151
Wicklow765909906128149159

Local strongholds in 1911

District Electoral Divisions (300+ residents) where O'Briens made up the largest share of the population. In Dromdaleague North, Co. Cork, about one resident in 7 was a O'Brien.

DEDCountyO'BriensShare
Dromdaleague NorthCork74 14.4%
KilglassLimerick51 11.4%
DoonKerry47 11.0%
DuntryleagueLimerick61 10.0%
DeerparkGalway61 9.1%
MocollopWaterford38 8.8%
TinnacrossWexford56 8.7%
TullaghortonTipperary41 8.7%

Origins

Septs & territories

Many Irish surnames were adopted independently by unrelated families. These are the distinct O'Brien lineages described in the sources.

A surname can point you towards a place. On its own, it cannot establish a pedigree.

Ó Briain of Thomond

Thomond (Tuadhmhumhain), centred on the modern County Clare · Clare, Limerick, Tipperary

This was the senior line, descended from Brian Boru. Its members were kings of Thomond, some were kings of Munster and two held the high kingship, though with opposition. After 1543 its heads became Earls of Thomond, and Bunratty Castle became their chief seat.[1][2][6]

O'Briens of Ara

Ara (Arra), north County Tipperary · Tipperary

Woulfe lists this as one of the principal branches. Its chief was styled Mac Í Bhriain Ara. Wikipedia notes that one later element in the O'Brien arms may refer to this branch.[1][2]

O'Briens of Coonagh

Coonagh, east County Limerick · Limerick

Woulfe names this as one of the branches into which the family divided.[1]

Mac Uí Bhriain of Pobal Bhriain

Pobal Bhriain (Pubblebrien), north County Limerick · Limerick

This branch took Carrigogunnell, on the Shannon, from the Ó Ciarmhaic family and made it its main stronghold. The barony takes its name, 'Brian's people', from the family.[1][7]

O'Briens of Aherlow

Aherlow, County Tipperary · Tipperary

Woulfe lists this as a separate branch of the family.[1]

O'Briens of Cumaragh

Cummeragh mountains, between Dungarvan and the Suir · Waterford

According to Woulfe, this branch held extensive lands along the Cummeragh mountains, including the valley running from Dungarvan towards the River Suir.[1]

O'Briens of Inchiquin and Dromoland

Inchiquin and Dromoland, County Clare · Clare

This line descends from Murrough, the last King of Thomond, who was made Baron Inchiquin in 1543. It later held a baronetcy and had its seat at Dromoland Castle. The Barony of Inchiquin is still held by the family.[2][8]

The name over time

History

Brian Boru and the Dál gCais

The O'Briens take their name from Brian Boru (c. 941–1014) of the Dál gCais, a people whose power base was the area of modern County Clare. Brian's father, Cennétig, was king of the Dál gCais, and his elder brother Mathgamain was the first of the family to take Cashel. Brian became King of Munster and then High King of Ireland. He was killed at the Battle of Clontarf on 23 April 1014 and buried at Armagh. Woulfe credits his victories over the Norse and their Irish allies with lifting his kin, the Uí Thoirdealbhaigh, to the leading place among the Dalcassians.[9][2][1]

Kings of Munster and Thomond

Brian's descendants called themselves Ua Briain, later Ó Briain. His grandson Toirdelbach and great-grandson Muirchertach were Kings of Munster and claimed the high kingship. In 1118 the Treaty of Glanmire divided Munster: Thomond went to the O'Briens and Desmond to the MacCarthys. The O'Briens supplied around thirty kings of Thomond until 1542. In 1276 the Norman Thomas de Clare was granted Thomond, but the de Clare claim ended with defeat at Dysert O'Dea in 1318.[2][10][11]

Earls of Thomond and Barons Inchiquin

In 1543 Murrough O'Brien, the last King of Thomond, surrendered his Gaelic kingship to Henry VIII. He was made Earl of Thomond and Baron Inchiquin. On his death in 1551 the earldom passed to a nephew, and the barony passed through his son Dermot. The earldom later became extinct, but the Inchiquin title passed to a distant cousin and survives. Conor O'Brien became the 19th Baron Inchiquin in 2023. With the new titles, inheritance of the peerages moved from Gaelic tanistry to primogeniture.[2][12]

Castles and seats

Bunratty Castle came into O'Brien hands around 1500 and became their chief seat in place of Ennis. Leamaneh Castle, on the edge of the Burren, began as a tower house built around 1480–90, probably by Toirdhealbhach Donn Ó Briain. It is linked with Máire Rua, who married Conor O'Brien in 1639. Dromoland Castle near Newmarket-on-Fergus was the home of the Barons Inchiquin. Donough O'Brien, 16th Baron, sold it in 1962 and it opened as a hotel the following year.[6][13][8][14]

Spread and confusion with other names

Woulfe noted that O'Brien had become one of the most common surnames in Ireland. He also recorded that it was once pronounced 'O'Breen'. Some O'Briens have no Dalcassian origin. The Westmeath family of Ó Braoin, lords of Brawney near Athlone, were often given the anglicised form O'Brien, which Woulfe calls incorrect. He gives this as an example of a rarer name being 'attracted' to a better-known one. Separately, a Brian family of Breton descent settled in Kilkenny and Wexford.[1][15][16][17]

Places linked to the name

  • Thomond (Tuamhain), Co. Clare — The O'Brien kingdom, centred on County Clare and taking in parts of Limerick and Tipperary.[18][2]
  • Bunratty Castle (Caisleán Bhun Raithe), Co. Clare — Held by the O'Briens from around 1500 and later the principal seat of the Earls of Thomond.[6]
  • Leamaneh Castle, Co. Clare — A tower house of around 1480–90, probably built by an O'Brien, later the home of Máire Rua.[13]
  • Dromoland Castle (Drom Ólainn), Co. Clare — Ancestral home of the O'Briens, Barons Inchiquin, until it was sold in 1962.[8]
  • Pubblebrien (Pobal Bhriain), Co. Limerick — A barony named after an O'Brien branch, whose stronghold was Carrigogunnell on the Shannon.[7][1]
  • Arra (Ara), Co. Tipperary — Territory of the O'Briens of Ara, whose chief was styled Mac Í Bhriain Ara.[1]

Everyday lives

The O'Briens in the census

Who the O'Briens were in the 1901 and 1911 censuses (and 1926 where recorded), set against everyone in Ireland in the same census.

O'Briens All of Ireland Ireland's figure marked on the O'Brien bar

Religion, 1911

Catholic +24.6 points vs Ireland
O'Briens 98.2%
All of Ireland 73.6%
Church of Ireland −11.9 points vs Ireland
O'Briens 1.3%
All of Ireland 13.2%
Presbyterian −10.0 points vs Ireland
O'Briens 0.1%
All of Ireland 10.1%
Methodist & other −2.8 points vs Ireland
O'Briens 0.3%
All of Ireland 3.1%

Irish language

Spoke Irish, 1901 +3.6 points vs Ireland
O'Briens 18.9%
All of Ireland 15.3%
Spoke Irish, 1911 +2.9 points vs Ireland
O'Briens 16.4%
All of Ireland 13.5%
Spoke Irish, 1926 · 26 counties −1.1 points vs Ireland
O'Briens 12.4%
All of Ireland 13.5%

183 O'Briens spoke Irish only in 1901.

Reading & writing

Could read and write, 1901 · aged 15+ about the same as Ireland
O'Briens 80.2%
All of Ireland 80.4%
Could read and write, 1911 · aged 15+ about the same as Ireland
O'Briens 86.0%
All of Ireland 85.8%

Family life, 1911

Household size · 6,330 households higher than Ireland
O'Briens 4.98
All of Ireland 4.83
Children born per mother · women 45–59 higher than Ireland
O'Briens 6.92
All of Ireland 6.46
Children still living −0.6 points vs Ireland
O'Briens 79.2%
All of Ireland 79.8%

Commonest occupations

Adults aged 15+, 1901 and 1911 combined.

Farmer4,787
Farmer's son2,396
Farmer's daughter1,408
General labourer1,338
Agricultural labourer1,288
Labourer1,066
Farm servant1,027
Domestic servant735
House keeper661
Farm labourer638

Born outside Ireland

1.2% of O'Briens in 1911 gave a birthplace outside Ireland.

England201
United States70
Scotland42
India31
Wales6
Australia & NZ6

Median age: 23 in 1901, 25 in 1911.

Given names

First names among the O'Briens

Men and boys

  1. John7,013
  2. Patrick5,496
  3. Michael4,419
  4. James4,027
  5. Thomas3,313
  6. William2,752
  7. Daniel1,187
  8. Denis1,123
  9. Timothy857
  10. Edward817

Women and girls

  1. Mary8,258
  2. Bridget3,581
  3. Margaret3,086
  4. Ellen2,702
  5. Kate1,809
  6. Catherine1,630
  7. Annie1,538
  8. Anne1,023
  9. Elizabeth966
  10. Julia966

All three censuses combined. Top five in 1926: John, Patrick, Michael, James, Thomas; Mary, Margaret, Bridget, Ellen, Annie.

Spellings

Spellings

This page combines the spellings below, which census enumerators and families used for the same name.

Spelling190119111926Records
O'Brien22,85024,56526,884Search
Brien8,2106,4573,254Search

Related forms

  • Brien — O'Brien without the O' prefix. Woulfe lists it among the anglicised forms of Ó Briain.[1]
  • O'Bryan, O'Brian, O'Bryen — Older and diaspora spellings of Ó Briain.[1][3]
  • MacBrien, MacBryan — Anglicised forms of Mac Bhriain, 'son of Brian'.[4]
  • O'Brien (for Ó Braoin) — In Westmeath, the unrelated Ó Braoin of Brawney were sometimes anglicised O'Brien. The usual forms are Breen and Bruen.[15]
  • Brian, Bryan — In Kilkenny and Wexford these can be a separate surname, from a Breton personal name brought to England at the Norman Conquest.[17]

Diaspora

The O'Briens abroad

Emigration carried the name worldwide. In the 2010 United States census:

SpellingPeopleUS rank
O'Brien118,557258th
Brien2,88211031st

Source: US Census Bureau, 2010 surname file (public domain).

Heraldry

Is there a O'Brien coat of arms?

Arms belonged to particular families, not to everyone named O'Brien. The Chief Herald of Ireland described the earliest O'Brien arms as a right forearm holding an upright sword, on red. After 1543 the Earls of Thomond bore English-style arms of three lions, and the sword-arm was kept as the crest. The associated motto is 'Lamh Laidir an Uachtar', 'the strong hand uppermost'.[2]

Websites selling a single “O'Brien family crest” are selling a design, not an inheritance. Arms in Ireland belonged to individuals and their heirs, and the Chief Herald of Ireland still grants arms that way today.

People

Notable people named O'Brien

  • Toirdelbach Ua Briain (1009–1086)
    Grandson of Brian Boru; King of Munster and effectively High King of Ireland.
  • Muirchertach Ua Briain (c. 1050–1119)
    King of Munster who declared himself High King of Ireland; great-grandson of Brian Boru.
  • Murrough O'Brien, 1st Earl of Thomond (died 1551)
    Last King of Thomond; surrendered his kingship to Henry VIII in 1543.
  • Murrough O'Brien, 1st Earl of Inchiquin (1614–1673)
    Munster soldier who held Ireland for Parliament in the 1640s, later joining the exiled Charles II.
  • Máire Rua O'Brien (1615/16–1686)
    Clare noblewoman of Leamaneh Castle; married three times to keep her family's lands.
  • William Smith O'Brien (1803–1864)
    Dromoland-born MP who led the failed Young Ireland rising of 1848 and was transported to Tasmania.
  • Charlotte Grace O'Brien (1845–1909)
    Author, nationalist activist and campaigner for the protection of female emigrants.
  • Kate O'Brien (1897–1974)
    Limerick-born novelist and playwright.
  • Conor Cruise O'Brien (1917–2008)
    Diplomat, politician, historian and writer; Minister for Posts and Telegraphs 1973–1977.
  • Vincent O'Brien (1917–2009)
    Cork-born racehorse trainer, voted the greatest influence in horse racing history in 2003.
  • Edna O'Brien (1930–2024)
    Novelist and short-story writer whose debut, The Country Girls, was banned in Ireland.
  • Conan O'Brien (born 1963)
    American television host, comedian and writer of Irish descent.

Questions

Questions about the O'Brien name

Is O'Brien an Irish surname?

Yes. O'Brien is the anglicised form of the Gaelic Ó Briain, 'descendant of Brian'. The family descends from Brian Boru, the Dál gCais king who became High King of Ireland and died at Clontarf in 1014. His descendants ruled Thomond, centred on County Clare, for centuries. A few Irish families of other origins took the same English spelling, such as the Ó Braoin of Westmeath.[1][2][15]

What is O'Brien in Irish?

The Irish form is Ó Briain, written Ua Briain in older Classical Irish. A woman is Ní Bhriain (daughter of an O'Brien) or Bean Uí Bhriain (wife of an O'Brien). Woulfe gives Síol mBriain as an old collective name for the O'Briens. Ó means 'grandson' or 'descendant', so the name means 'descendant of Brian'.[2][3][19][9]

How do you pronounce O'Brien?

In English it is usually 'oh-BRY-en', though in Britain the first syllable is often lighter, closer to 'uh-BRY-en'. Woulfe recorded that it was originally pronounced 'O'Breen', which is closer to the Irish. The Irish Ó Briain sounds roughly like 'oh BREE-in', with a slender r.[20][16][2]

Is there an O'Brien family crest or coat of arms?

There is no crest belonging to everyone called O'Brien. Arms were borne by particular families, chiefly the heads of the house. The Chief Herald of Ireland described the first O'Brien arms as a right forearm holding a sword, on red. From 1543 the Earls of Thomond used arms of three lions, and the sword-arm survived as their crest.[2]

What is the O'Brien clan motto?

The motto associated with the O'Brien arms is 'Lamh Laidir an Uachtar', usually translated 'the strong hand uppermost'. It goes with the sword-arm crest of the heads of the family, the Earls of Thomond and later the Barons Inchiquin. It is not a motto that every O'Brien has a right to as a personal device.[2]

Where does the O'Brien name come from?

The name comes from Thomond, the Dál gCais homeland around County Clare. Woulfe says the family's lands took in all of Clare and large parts of Limerick, Tipperary and Waterford. The family divided into several branches, at Ara, Coonagh, Pobal Bhriain, Aherlow and Cumaragh, which helps explain why the name became common across Munster.[1][18]

Are Brien and O'Brien the same name?

Usually, yes. Brien is O'Brien without the O' prefix, and Woulfe lists both as anglicised forms of Ó Briain. Woulfe notes that most Irish surnames lost their O' or Mac at some point during anglicisation. In Kilkenny and Wexford, however, Brian or Bryan can be a separate surname of Breton origin.[1][16][17]

Where in Ireland is the O'Brien surname most common?

In the 1911 census the largest numbers of O'Briens lived in Cork (5,957), Dublin (4,169), Tipperary (3,231). Relative to population, the name was most concentrated in Tipperary (212 per 10,000), Limerick (189 per 10,000), Waterford (182 per 10,000).

How common was the O'Brien surname in Ireland?

31,022 people were recorded as O'Brien or Brien in the 1911 census of Ireland, making it the 7th most common surname. That is roughly 0.7% of the population, or 1 person in 141.

Looking for a O'Brien ancestor?

Search every O'Brien household in the 1901, 1911 and 1926 censuses, with free images of the original forms.

Search records on irishcensus.com

Evidence

Sources

  1. Patrick Woulfe, Ó Briain (1923). Sloinnte Gaedheal is Gall: Irish Names and Surnames
  2. Wikipedia contributors, O'Brien dynasty (2026)
  3. Wikipedia contributors, O'Brien (surname) (2026)
  4. Patrick Woulfe, Mac Bhriain (1923). Sloinnte Gaedheal is Gall: Irish Names and Surnames
  5. Wikipedia contributors, Brian (given name) (2026)
  6. Wikipedia contributors, Bunratty Castle (2026)
  7. Wikipedia contributors, Pubblebrien (2026)
  8. Wikipedia contributors, Dromoland Castle (2026)
  9. Wikipedia contributors, Brian Boru (2026)
  10. Wikipedia contributors, Toirdelbach Ua Briain (2026)
  11. Wikipedia contributors, Muirchertach Ua Briain (2026)
  12. Wikipedia contributors, Murrough O'Brien, 1st Earl of Thomond (2026)
  13. Wikipedia contributors, Leamaneh Castle (2026)
  14. Wikipedia contributors, Máire Rua O'Brien (2026)
  15. Patrick Woulfe, Ó Braoin (1923). Sloinnte Gaedheal is Gall: Irish Names and Surnames
  16. Patrick Woulfe, Anglicisation of Irish Surnames (1923). Introductory chapter of Irish Names and Surnames
  17. Patrick Woulfe, Brian (1923). Sloinnte Gaedheal is Gall: Irish Names and Surnames
  18. Wikipedia contributors, Thomond (2026)
  19. Patrick Woulfe, Declension of Irish Surnames (1923). Introductory chapter of Irish Names and Surnames
  20. Wiktionary contributors, O'Brien (2026)
  21. Census of Ireland 1901 and 1911, and Census of Population 1926, National Archives of Ireland. Counts compiled by surnames.ie from the irishcensus.com transcription (dataset 20260831130351). 1926 data © National Archives of Ireland, CC BY 4.0.
  22. Irish forms cross-checked against Gaois surname data (Fiontar & Scoil na Gaeilge, DCU).

How we compile these figures: methodology.