surnames.ie

Irish surname · 25th most common in 1911

Brennan

Also spelt O'Brennan

Brennan is the English form of several Irish surnames. Most common is Ó Braonáin, 'descendant of Braonán', whose leading sept ruled Uí Duach (Idough) in north Kilkenny. In Ulster it usually represents Ó Branáin, and in Roscommon Mac Branáin, both from Branán, 'little raven'.

Irish Ó BraonáinIrish Ó BranáinIrish Mac Branáin
1901 census
14,707
#27 · 33 per 10,000
1911 census
14,630
#25 · 33 per 10,000
1926 census
14,039
#17 · 47 per 10,000
Most numerous
Kilkenny
Highest share: Kilkenny

Language & meaning

Meaning & Irish forms

Gaelic Gaelic Irish: several unrelated septs called Ó Braonáin, Ó Branáin and Mac Branáin, whose English forms merged as Brennan.[1][2][3]

Ó Braonáin
“descendant of Braonán”[1][4][5]
The usual source of Brennan outside Ulster, borne by several unrelated septs. The feminine form appears in the Irish name of the singer Enya, Eithne Ní Bhraonáin.
Ó Branáin
“descendant of Branán”[2][4]
Woulfe says this is generally the origin of the name in Ulster; it also gives Brannan and Brannon.
Mac Branáin
“son of Branán”[3][4]
The Roscommon family of Corca Achlann. Woulfe remarks that Brennan is a common but not strictly correct English form of it.

The name is built on the personal name Braonán, usually explained as “a diminutive of braon, 'a drop' or 'moisture'”. Woulfe calls Braonán a diminutive of Braon; Wikipedia links it to the word for a drop or moisture. The separate name Branán is a diminutive of bran, 'a raven'.[1][4][2]

Pronunciation

Brennan: BREN-un

Place

Where the Brennans 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: 27.1 per 10,000 (457 people) Waterford: 13.6 per 10,000 (112 people) Dublin: 38.9 per 10,000 (1,868 people) Kilkenny: 251.5 per 10,000 (1,888 people) Carlow: 140.4 per 10,000 (510 people) Limerick: 17.4 per 10,000 (250 people) Louth: 37.9 per 10,000 (239 people) Tipperary: 25.5 per 10,000 (389 people) Roscommon: 98.1 per 10,000 (922 people) Meath: 20.7 per 10,000 (135 people) Wicklow: 31.9 per 10,000 (194 people) Cavan: 12.8 per 10,000 (117 people) Cork: 10.3 per 10,000 (403 people) Clare: 25.4 per 10,000 (265 people) Galway: 29.3 per 10,000 (534 people) Mayo: 54 per 10,000 (1,037 people) Sligo: 151.8 per 10,000 (1,201 people) Leitrim: 19 per 10,000 (120 people) Offaly: 21.6 per 10,000 (123 people) Laois: 130.8 per 10,000 (716 people) Kildare: 49.3 per 10,000 (330 people) Kerry: 34.7 per 10,000 (555 people) Monaghan: 52.8 per 10,000 (378 people) Wexford: 38.4 per 10,000 (393 people) Longford: 30.3 per 10,000 (133 people) Westmeath: 44.4 per 10,000 (267 people) Tyrone: 4.8 per 10,000 (69 people) Antrim: 10 per 10,000 (480 people) Armagh: 9.8 per 10,000 (117 people) Fermanagh: 6.3 per 10,000 (38 people) Londonderry: 8.7 per 10,000 (122 people) Down: 8.8 per 10,000 (268 people)
fewerup to 263 per 10,000

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

Highest concentration · 1911

Kilkenny

252 per 10,000

1,888 Brennans · 7.55× the national share

Highest share, 1911

  1. Kilkenny 252
  2. Sligo 152
  3. Carlow 140
  4. Laois 131
  5. Roscommon 98
  6. Mayo 54
  7. Monaghan 53
  8. Kildare 49

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
Antrim416480—910—
Armagh150117—1210—
Carlow571510511153140149
Cavan95117126101315
Clare267265234242525
Cork36840346891013
Donegal461457452272730
Down199268—79—
Dublin1,5541,8682,346353947
Fermanagh5438—86—
Galway549534578292934
Kerry563555477343532
Kildare332330325544956
Kilkenny1,9251,8881,860255252263
Laois806716782141131152
Leitrim109120111161920
Limerick182250271121719
Londonderry99122—79—
Longford120133120263030
Louth267239331413853
Mayo1,0011,0371,009515458
Meath183135182262129
Monaghan448378451605369
Offaly153123159252230
Roscommon1,1059227841109894
Sligo1,2241,2011,001152152141
Tipperary354389431222631
Tyrone9269—65—
Waterford121112119141415
Westmeath285267272464448
Wexford478393435463846
Wicklow176194204293236

Local strongholds in 1911

District Electoral Divisions (300+ residents) where Brennans made up the largest share of the population. In Moneenroe, Co. Kilkenny, about one resident in 5 was a Brennan.

DEDCountyBrennansShare
MoneenroeKilkenny339 18.6%
FarnansLaois45 14.7%
ClogharinkaKilkenny45 12.5%
CloghKilkenny196 11.8%
LeitrimSligo112 11.0%
DysartgallenLaois43 10.2%
AnnayallaMonaghan104 10.0%
ArdoughLaois42 9.4%

Origins

Septs & territories

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

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

Ó Braonáin of Uí Duach (Idough)

Uí Duach, now largely the barony of Fassadinin · Kilkenny

The best-known Brennan sept, chiefs of Uí Duach in the kingdom of Osraige (Ossory). Wikipedia describes them as a junior branch of the Ossory royal line, though Dubhaltach Mac Fhirbhisigh's genealogies, followed by some modern scholars, place them among the Uí Failghe instead. They kept a striking degree of independence until 1635, when their remaining lands passed to Sir Christopher Wandesforde.[1][4][6]

Ó Braonáin of Crevagh

Crevagh · Westmeath

Woulfe describes this as a numerous and powerful clan in Co. Westmeath, but gives no further history.[1]

Ó Braonáin of Síol Anmchadha

barony of Longford, south-east Co. Galway · Galway

Of the same stock as the O'Maddens of Síol Anmchadha. Woulfe notes they were still numerous at the end of the 16th century.[1]

Ó Braonáin of Dunkerron

Dunkerron · Kerry

Followers of O'Sullivan Mór, whom Woulfe found still numerous in Kerry.[1]

Ó Branáin of Ulster

churches of Derry and Derryvullan · Derry, Fermanagh

A church family who were erenaghs, hereditary stewards of church land, at Derry and at Derryvullan in Co. Fermanagh. Woulfe thought they were also known as Ó Branagáin.[2]

Mac Branáin of Corca Achlann

Corca Achlann · Roscommon

A leading Roscommon family whose head was chief of Corca Achlann. Tradition made them descendants of Ona, said to have given St Patrick the site of the church at Elphin, and Woulfe thought the hereditary erenaghs of Elphin were a branch of the family.[3]

The name over time

History

Several names, one spelling

Brennan gathers together at least three Gaelic surnames. Ó Braonáin, from the personal name Braonán, belonged to several unrelated septs in Kilkenny, Westmeath, Galway and Kerry. Ó Branáin and Mac Branáin come from a different name, Branán, 'little raven'. Woulfe admitted it was almost impossible to tell their English forms apart, since the same spellings served both. His rule of thumb was that Ó Branáin is the usual origin in Ulster and Ó Braonáin in the other three provinces, while Mac Branáin belongs to Roscommon.[1][2][3][4]

The O'Brennans of Idough

The most prominent Brennans were the O'Brennans of Uí Duach, anglicised Idough, in the north of Co. Kilkenny. Wikipedia describes them as a junior sept of the Osraige royal house, descended from a younger son of Cerball mac Dúnlainge, king of Ossory, who died in 888. The 17th-century genealogist Dubhaltach Mac Fhirbhisigh placed them among the Uí Failghe instead, a view the modern scholar Bart Jaski supports. Their territory was later known as the cantred of Odogh or of the Comar, after the old name of Castlecomer.[4][6][7][1]

Holding out until 1635

O'Heerin's topographical poem, composed around 1420, assigns Uí Duach to the O'Brennans as it stood at the time of the Norman invasion. The family held on to the district with notable persistence for centuries afterwards. In 1635 the town of Castlecomer and the remaining Brennan lands were handed to Sir Christopher Wandesforde, and the Wandesfords were based in the barony from then on. Woulfe noted that the name was still very common in north Kilkenny in his day.[6][1]

Other Ó Braonáin septs

Woulfe described three further Ó Braonáin families with no known connection to Idough. One, at Crevagh in Co. Westmeath, he called numerous and powerful. Another belonged to Síol Anmchadha, the O'Madden country in the barony of Longford in south-east Galway, and was still numerous there at the end of the 16th century. A third, in Dunkerron in Co. Kerry, followed O'Sullivan Mór. This scattering helps explain why Brennan is found so widely across Leinster, Connacht and Munster.[1]

The MacBrennans of Roscommon and the Ulster Brennans

In Roscommon the Mac Branáin family were chiefs of Corca Achlann. Tradition held that their ancestor was Ona, who granted St Patrick the site of the church of Elphin, and Woulfe believed the Uí Branáin who were erenaghs, or hereditary church stewards, at Elphin were a branch of the same family. In Ulster, Ó Branáin was the name of an erenagh family at the churches of Derry and Derryvullan in Fermanagh. Burke records a separate coat of arms for an 'O'Brenon' sept of Ulster and Connacht.[3][2][8]

Places linked to the name

  • Fassadinin (Idough) (Uí Duach), Co. Kilkenny — The barony that largely corresponds to Uí Duach, the O'Brennan territory.[6][1]
  • Castlecomer, Co. Kilkenny — Town at the heart of Idough, handed with the last Brennan lands to Sir Christopher Wandesforde in 1635.[6]
  • Elphin, Co. Roscommon — Its church site was traditionally granted to St Patrick by Ona, ancestor of the Mac Branáin family; the Uí Branáin were erenaghs there.[3]
  • Derryvullan, Co. Fermanagh — Church where the Ó Branáin family were erenaghs.[2]
  • Cloneen and Moneenroe, Co. Kilkenny — Seats of the O'Brenan family recorded by Burke as chiefs of the name.[8]

Everyday lives

The Brennans in the census

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

Brennans All of Ireland Ireland's figure marked on the Brennan bar

Religion, 1911

Catholic +22.5 points vs Ireland
Brennans 96.1%
All of Ireland 73.6%
Church of Ireland −11.1 points vs Ireland
Brennans 2.1%
All of Ireland 13.2%
Presbyterian −8.7 points vs Ireland
Brennans 1.4%
All of Ireland 10.1%
Methodist & other −2.7 points vs Ireland
Brennans 0.4%
All of Ireland 3.1%

Irish language

Spoke Irish, 1901 about the same as Ireland
Brennans 15.5%
All of Ireland 15.3%
Spoke Irish, 1911 +0.9 points vs Ireland
Brennans 14.4%
All of Ireland 13.5%
Spoke Irish, 1926 · 26 counties about the same as Ireland
Brennans 13.1%
All of Ireland 13.5%

85 Brennans spoke Irish only in 1901.

Reading & writing

Could read and write, 1901 · aged 15+ about the same as Ireland
Brennans 80.5%
All of Ireland 80.4%
Could read and write, 1911 · aged 15+ +0.9 points vs Ireland
Brennans 86.7%
All of Ireland 85.8%

Family life, 1911

Household size · 3,074 households lower than Ireland
Brennans 4.75
All of Ireland 4.83
Children born per mother · women 45–59 higher than Ireland
Brennans 6.92
All of Ireland 6.46
Children still living +1.6 points vs Ireland
Brennans 81.4%
All of Ireland 79.8%

Commonest occupations

Adults aged 15+, 1901 and 1911 combined.

Farmer3,194
Farmer's son1,537
Farmer's daughter831
Agricultural labourer456
General labourer445
Labourer356
Farm servant352
Farm labourer314
House keeper313
Farmer's wife226

Born outside Ireland

1.1% of Brennans in 1911 gave a birthplace outside Ireland.

England85
Scotland31
United States30
Australia & NZ5
India3
Wales3

Median age: 23 in 1901, 25 in 1911.

Given names

First names among the Brennans

Men and boys

  1. John3,334
  2. Patrick2,700
  3. James2,330
  4. Michael2,003
  5. Thomas1,842
  6. William759
  7. Edward640
  8. Martin567
  9. Joseph545
  10. Peter452

Women and girls

  1. Mary3,713
  2. Bridget1,814
  3. Margaret1,240
  4. Ellen1,006
  5. Catherine917
  6. Annie851
  7. Kate848
  8. Anne654
  9. Elizabeth526
  10. Maggie423

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

Spellings

Spellings

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

Spelling190119111926Records
Brennan14,69714,61114,015Search
O'Brennan101924Search

Related forms

  • O'Brennan — The form keeping the Ó prefix.[1]
  • Brenan, O'Brenan — The spelling used by the Kilkenny chiefs in Burke's General Armory.[8]
  • Brannan, Brannon — Mostly from Ó Branáin or Mac Branáin, though Woulfe warns the forms overlap.[2][3]
  • Brinan, Brinane — Older spellings of Ó Braonáin.[1]
  • MacBrennan — From Mac Branáin of Roscommon; Woulfe records early forms such as M'Brenan.[3]
  • Ní Bhraonáin — The Irish form used by women, as in the name of the singer Enya.[5]

Diaspora

The Brennans abroad

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

SpellingPeopleUS rank
Brennan49,238701st

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

Heraldry

Is there a Brennan coat of arms?

Arms were granted to particular families, so there is no single Brennan crest. Burke's General Armory records arms for O'Brenan of Cloneen and Moneenroe, Co. Kilkenny, styled chief of his name: on red, two lions rampant facing each other and supporting a gold sheaf, with three swords above, and the motto 'Sub hoc signo vinces'. Burke notes that these arms were allowed in 1769 to John O'Brenan of Malaga in Spain, and records different arms for an O'Brenon sept of Ulster and Connacht.[8]

Websites selling a single “Brennan 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 Brennan

  • Joseph Brenan (1828–1857)
    Poet, journalist and leading member of Young Ireland and the Irish Confederation.
  • Louis Brennan (1852–1932)
    Irish-Australian engineer who invented the Brennan torpedo, an early wire-guided torpedo.
  • Christopher Brennan (1870–1932)
    Australian poet, scholar and literary critic.
  • Úna Brennan (1888–1958)
    Irish republican and feminist active in the 1916 Rising and the revolutionary years.
  • Walter Brennan (1894–1974)
    American actor, the only person to win three Academy Awards for best supporting actor.
  • William J. Brennan Jr. (1906–1997)
    US Supreme Court justice from 1956 to 1990 and a leader of its liberal wing.
  • Maeve Brennan (1917–1993)
    Irish short-story writer and journalist who made her career in the United States.
  • Gerard Brennan (1928–2022)
    Chief Justice of Australia who wrote the lead judgment in the Mabo case.
  • Séamus Brennan (1948–2008)
    Fianna Fáil minister who held transport, social affairs and arts portfolios.
  • Moya Brennan (1952–2026)
    Folk singer, songwriter and harpist who performed with the family band Clannad from 1970.
  • Enya (Eithne Ní Bhraonáin) (born 1961)
    Singer and composer, the best-selling Irish solo artist.
  • Eddie Brennan (born 1978)
    Kilkenny hurler for twelve seasons and later Laois manager.

Questions

Questions about the Brennan name

Is Brennan an Irish surname?

Yes. Brennan is an English form of several Gaelic Irish surnames, chiefly Ó Braonáin, with Ó Branáin and Mac Branáin also contributing. The best-known family were the O'Brennans of Idough in north Kilkenny, but there were separate septs in Westmeath, Galway, Kerry, Ulster and Roscommon, which is why the name is spread so widely.[1][2][3]

What is Brennan in Irish?

Usually Ó Braonáin, 'descendant of Braonán'; a woman uses Ní Bhraonáin, as in the Irish name of the singer Enya. In Ulster, Brennan is more often from Ó Branáin, and in Roscommon from Mac Branáin, both meaning a descendant or son of Branán.[1][2][3][5]

What does the name Brennan mean?

It depends on the family. Braonán, behind Ó Braonáin, is a diminutive of Braon, which Wikipedia connects with a word for a drop or moisture. Branán, behind Ó Branáin and Mac Branáin, is a diminutive of bran, 'a raven'. In each case the surname means 'descendant' or 'son' of a man with that name.[1][2][4]

Are Brennan, Brannan and Brannon the same name?

Often, but not always. Woulfe found the English forms of Ó Braonáin and Ó Branáin so mixed that the two can rarely be told apart. Brannan and Brannon lean towards Ó Branáin and Mac Branáin, and Brennan towards Ó Braonáin, but any of these spellings may be found in a family of either origin.[1][2]

Is there a Brennan family crest or coat of arms?

Not one for everyone named Brennan. Burke records arms for the O'Brenans of Cloneen and Moneenroe in Co. Kilkenny, with the motto 'Sub hoc signo vinces' ('In this sign you will conquer'), allowed in 1769 to a member of the family living in Spain. He records different arms for an O'Brenon sept of Ulster and Connacht. Each belonged to a particular family.[8]

Where does the Brennan name come from?

The best-known Brennans came from Uí Duach, or Idough, in north Co. Kilkenny, around Castlecomer, where they held their lands until 1635. Other families of the name were rooted in Westmeath, south-east Galway and Kerry (all Ó Braonáin), in Roscommon (Mac Branáin) and in Ulster (Ó Branáin), so a family's county is an important clue.[6][1][2][3]

Where in Ireland is the Brennan surname most common?

In the 1911 census the largest numbers of Brennans lived in Kilkenny (1,888), Dublin (1,868), Sligo (1,201). Relative to population, the name was most concentrated in Kilkenny (252 per 10,000), Sligo (152 per 10,000), Carlow (140 per 10,000).

How common was the Brennan surname in Ireland?

14,630 people were recorded as Brennan or O'Brennan in the 1911 census of Ireland, making it the 25th most common surname. That is roughly 0.3% of the population, or 1 person in 300.

Looking for a Brennan ancestor?

Search every Brennan 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 Braonáin, in Irish Names and Surnames (1923)
  2. Patrick Woulfe, Ó Branáin, in Irish Names and Surnames (1923)
  3. Patrick Woulfe, Mac Branáin, in Irish Names and Surnames (1923)
  4. Wikipedia, Brennan (surname) (2026)
  5. Wikipedia, Enya (2026)
  6. Wikipedia, Fassadinin (2026)
  7. Wikipedia, Cerball mac Dúnlainge (2026)
  8. Sir Bernard Burke, The General Armory of England, Scotland, Ireland, and Wales (1884). Entries 'Brenan, or O'Brenan', 'O'Brenan' and 'O'Brenon'.
  9. 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.
  10. Irish forms cross-checked against Gaois surname data (Fiontar & Scoil na Gaeilge, DCU).

How we compile these figures: methodology.