Language & meaning
Meaning & Irish forms
Gaelic Gaelic Irish: a patronymic surname taken independently by a Dál gCais family in Thomond (Clare) and by the ruling family of Oriel (Monaghan), with a smaller Fermanagh family besides.[1][2][3]
The name is built on the personal name Mathghamhain, usually explained as “bear”. Woulfe glosses the personal name as 'bear', and Wikipedia renders the surname as 'son of the bear'. The same name lies behind O'Mahony.[1][5][2]
Pronunciation
McMahon: mək-MAN or mək-MAHN; in Ireland also mək-MA-hən
Place
Where the McMahons 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.
Share of each county's census population. 1926 covers the 26 counties of the Irish Free State only.
Highest concentration · 1901
Clare
276 per 10,000
3,102 McMahons · 12.75× the national share
Highest share, 1901
Per 10,000 residents. A concentration index above 1 means the name was commoner there than nationally.
Highest concentration · 1911
Clare
284 per 10,000
2,967 McMahons · 13.02× the national share
Highest share, 1911
Per 10,000 residents. A concentration index above 1 means the name was commoner there than nationally.
County figures as a table
| County | 1901 | 1911 | 1926 | Per 10k 1901 | Per 10k 1911 | Per 10k 1926 |
|---|---|---|---|---|---|---|
| Antrim | 347 | 369 | — | 8 | 8 | — |
| Armagh | 414 | 383 | — | 33 | 32 | — |
| Carlow | 14 | 6 | 3 | 4 | 2 | 1 |
| Cavan | 303 | 324 | 322 | 31 | 36 | 39 |
| Clare | 3,102 | 2,967 | 2,709 | 276 | 284 | 285 |
| Cork | 183 | 191 | 187 | 5 | 5 | 5 |
| Donegal | 68 | 84 | 76 | 4 | 5 | 5 |
| Down | 394 | 400 | — | 14 | 13 | — |
| Dublin | 764 | 880 | 1,055 | 17 | 18 | 21 |
| Fermanagh | 354 | 334 | — | 55 | 55 | — |
| Galway | 59 | 77 | 105 | 3 | 4 | 6 |
| Kerry | 376 | 362 | 355 | 23 | 23 | 24 |
| Kildare | 34 | 38 | 57 | 6 | 6 | 10 |
| Kilkenny | 11 | 22 | 12 | 2 | 3 | 2 |
| Laois | 86 | 64 | 40 | 15 | 12 | 8 |
| Leitrim | 20 | 5 | 18 | 3 | 1 | 3 |
| Limerick | 922 | 948 | 894 | 63 | 66 | 64 |
| Londonderry | 67 | 71 | — | 5 | 5 | — |
| Longford | 11 | 5 | 0 | 2 | 1 | 0 |
| Louth | 129 | 160 | 195 | 20 | 25 | 31 |
| Mayo | 20 | 35 | 23 | 1 | 2 | 1 |
| Meath | 186 | 201 | 182 | 27 | 31 | 29 |
| Monaghan | 1,123 | 1,003 | 1,036 | 151 | 140 | 159 |
| Offaly | 39 | 36 | 58 | 7 | 6 | 11 |
| Roscommon | 2 | 15 | 17 | 0 | 2 | 2 |
| Sligo | 7 | 13 | 21 | 1 | 2 | 3 |
| Tipperary | 174 | 158 | 143 | 11 | 10 | 10 |
| Tyrone | 316 | 325 | — | 21 | 23 | — |
| Waterford | 22 | 10 | 6 | 3 | 1 | 1 |
| Westmeath | 16 | 27 | 10 | 3 | 5 | 2 |
| Wexford | 25 | 29 | 22 | 2 | 3 | 2 |
| Wicklow | 14 | 35 | 29 | 2 | 6 | 5 |
Local strongholds in 1911
District Electoral Divisions (300+ residents) where McMahons made up the largest share of the population. In Rinealon, Co. Clare, about one resident in 6 was a McMahon.
| DED | County | McMahons | Share |
|---|---|---|---|
| Rinealon | Clare | 74 | 17.2% |
| Kiltoraght | Clare | 72 | 12.9% |
| Knocknaboley | Clare | 96 | 11.3% |
| Tullig | Clare | 33 | 10.3% |
| Loughea | Clare | 37 | 9.1% |
| Dresternan | Fermanagh | 72 | 9.1% |
| Ayle | Clare | 39 | 9.0% |
| Spancelhill | Clare | 34 | 8.0% |
Origins
Septs & territories
Many Irish surnames were adopted independently by unrelated families. These are the distinct McMahon lineages described in the sources.
A surname can point you towards a place. On its own, it cannot establish a pedigree.
Mac Mathghamhna of Corca Baiscinn (Thomond)
Corca Baiscinn, the baronies of Moyarta and Clonderalaw · Clare
A branch of the O'Briens, named from Mahon, a son of Muirchertach Mór O'Brien, who was king of Ireland from 1094 to 1119. Wikipedia describes them taking Corcu Baiscind from its older rulers in the 12th century, around the time the surname became fixed. After 1488 the lordship was split between a western line at Moyarta and an eastern line at Clonderalaw, with castles at Carrigaholt and Clonderlaw.[1][3][6]
Mac Mathghamhna of Oriel (Airgíalla)
Oriel, later Co. Monaghan, including Farney and Dartree · Monaghan
Woulfe ranks them among the most powerful families of Ulster. They rose as the O'Carrolls declined in the 13th century and Wikipedia lists them as kings of Oriel from 1243 to 1590, tracing their descent to the Three Collas. Burke places their chief seat at Dartree and calls them kin of the Maguires of Fermanagh. They kept land and influence in Monaghan until the wars of the 1640s.[1][3][7]
McMahon of Fermanagh
Co. Fermanagh · Fermanagh
Wikipedia notes a separate McMahon family in Fermanagh descended from Mahon Maguire, a grandson of Donn Carrach Maguire. Woulfe does not describe it.[3]
Ó Mathghamhna of Ulidia
Ulidia (Ulaid), east Ulster · Down
Woulfe describes an Ó Mathghamhna family that was powerful in Ulidia in the 11th and 12th centuries and was still found in Co. Down and elsewhere in east Ulster, where its name had become Mahon or MacMahon. Wikipedia, citing John O'Hart, likewise says early MacMahons, sometimes called O'Mahons, were chiefs in Ulaid.[5][3]
The name over time
History
Two families, one name
Mac Mathghamhna means 'son of Mathghamhain', a personal name meaning 'bear', and in modern Irish it is written Mac Mathúna. Woulfe identified two great families of the name with no common ancestry. One, in Clare, belonged to the Dál gCais and took its name from a son of the O'Brien high king Muirchertach. The other ruled Oriel, the Airgíalla kingdom that became Co. Monaghan. Wikipedia dates the surname in both places to about the 11th century. A third, smaller family in Fermanagh descended from the Maguires, so a McMahon family's home county is the first clue to which line it belongs.[1][2][3][4]
Lords of Corca Baiscinn
The Clare MacMahons claimed descent from Mahon O'Brien, who, according to the historian Frost as cited by Wikipedia, died in 1129. In the 12th century his descendants seized Corcu Baiscind, the south-western corner of Clare, from the line of Cairbre Baschaín, and Woulfe defines their patrimony as the baronies of Moyarta and Clonderalaw. When Donogh MacMahon, lord of Corca Baiscinn, died in 1488, the territory was divided: Brian MacMahon took the western half, known as Moyarta, and Teige Roe the eastern half, Clonderalaw. The tower house at Carrigaholt, on the Shannon estuary, was built by the MacMahons around 1480.[3][6][1][8]
Armada, Kinsale and Cromwell
In 1585 the heads of both MacMahon lines signed a deed of composition with the Lord Deputy, Sir John Perrot, and were allowed to keep their castles and lands. In September 1588 seven ships of the Spanish Armada anchored off Carrigaholt; Teige Caech MacMahon refused them help, yet the castle was besieged soon afterwards, and in 1589 the Earl of Thomond took it and hanged the garrison. Sources differ on the end of the western line in 1602: Wikipedia says its last chief died at or soon after Kinsale, while Woulfe says he was killed by accident by his own son at Bearhaven. The eastern line survived until Ireton seized Clonderlaw Castle in 1651.[3][8][1]
The MacMahons of France
After the Gaelic defeats of the 17th century, many Clare MacMahons took service in the Irish Brigade of the French army. The best-known descendant was Patrice de MacMahon, Duke of Magenta and Marshal of France, who was President of the French Republic from 1873 to 1879. Burke records that arms were allowed in 1750 to the marshal's ancestor, John Baptist MacMahon, son of Patrick MacMahon of Torrodile in Co. Limerick, whose line he traced to the lords of Clonderlaw. Wikipedia notes that the family is still prominent in France, with its home at the Château de Sully near Dijon.[3][9][7][1]
Kings of Oriel
The Monaghan MacMahons traced their line through Clann Nadsluaigh to the Three Collas and to Mathgamain, lord of Fernmag, the district now called Farney. Woulfe says they rose as the O'Carrolls declined in the 13th century, and they held the kingship of Oriel until 1590. In 1585 Rossa Buidhe MacMahon agreed to surrender his lands and receive them back from the Crown, and the territory became Co. Monaghan. Of its five baronies, Wikipedia says MacMahons controlled Farney, Cremorne, Dartree and Monaghan, while Truagh went to the McKennas. Burke places the family's chief seat at Dartree.[3][10][1][11][7]
1641 and the churchmen of Oriel
The Oriel MacMahons lost Monaghan after the rising of 1641. Colonel Hugh Oge MacMahon was party to the plan to seize Dublin Castle, which failed after he let it slip to his foster brother Owen Connolly. He was taken to the Tower of London, escaped in August 1644, was recaptured and beheaded in London that November. Elsewhere MacMahons took Castleblayney and Carrickmacross. Woulfe also notes the family's churchmen: Heber MacMahon was both bishop of Clogher and a general in Ulster, and three MacMahons in succession were archbishops of Armagh in the early 18th century, among them Hugh and Bernard MacMahon.[3][1][12][13][14]
Places linked to the name
- Carrigaholt, Co. Clare — Its tower house was built around 1480 by the MacMahons of Corca Baiscinn and held by Teige Caech MacMahon in 1588.[8][3]
- Clonderalaw (Cluain idir Dhá Lá), Co. Clare — Barony of the eastern MacMahon lordship, whose castle Ireton seized in 1651.[15][3][1]
- Moyarta (Maigh Fhearta), Co. Clare — Barony on the Loop Head peninsula, seat of the western MacMahon lordship.[16][3][1]
- Farney (Fearnaigh), Co. Monaghan — Named from the kingdom of Fernmag, whose lord Mathgamain was the Oriel MacMahons' namesake; later a MacMahon barony.[11][3]
- Dartree (Dartraí), Co. Monaghan — Barony that Burke names as the chief seat of the Oriel MacMahons.[17][7][3]
Everyday lives
The McMahons in the census
Who the McMahons were in the 1901 and 1911 censuses (and 1926 where recorded), set against everyone in Ireland in the same census.
McMahons All of Ireland Ireland's figure marked on the McMahon bar
Religion, 1911
Irish language
27 McMahons spoke Irish only in 1901.
Reading & writing
Family life, 1911
Commonest occupations
Adults aged 15+, 1901 and 1911 combined.
| Farmer | 2,045 |
| Farmer's son | 994 |
| Farmer's daughter | 513 |
| General labourer | 285 |
| Farm servant | 258 |
| Agricultural labourer | 234 |
| Labourer | 201 |
| House keeper | 199 |
| Housekeeper | 158 |
| Domestic servant | 155 |
Born outside Ireland
1.6% of McMahons in 1911 gave a birthplace outside Ireland.
| England | 69 |
| Scotland | 39 |
| United States | 33 |
| Australia & NZ | 5 |
| India | 5 |
| Wales | 2 |
Median age: 24 in 1901, 25 in 1911.
Given names
First names among the McMahons
Men and boys
- John1,956
- Patrick1,778
- Michael1,285
- James1,209
- Thomas1,003
- Peter361
- Joseph319
- William275
- Martin259
- Francis253
Women and girls
- Mary2,281
- Bridget1,206
- Margaret867
- Ellen602
- Catherine550
- Annie434
- Kate389
- Anne364
- Elizabeth282
- Maggie239
All three censuses combined. Top five in 1926: John, Patrick, Michael, James, Thomas; Mary, Bridget, Margaret, Annie, Ellen.
Spellings
Spellings
This page combines the spellings below, which census enumerators and families used for the same name.
| Spelling | 1901 | 1911 | 1926 | Records |
|---|---|---|---|---|
| McMahon | 9,137 | 9,074 | 7,166 | Search |
| MacMahon | 465 | 503 | 409 | Search |
Related forms
- MacMahon — The fuller spelling of the same name; Woulfe and Wikipedia use it alongside McMahon.[1][2]
- MacMaghon, MacMaghone, MacMachon, MacMahan — Older English spellings of Mac Mathghamhna recorded by Woulfe.[1]
- MacMann — Another anglicised form Woulfe lists under Mac Mathghamhna.[1]
- Mahon, Mahony — Forms that can come from either Mac Mathghamhna or Ó Mathghamhna.[1][5]
- Matthews, Mathews — English names Woulfe records as occasionally substituted for Mac Mathghamhna.[1]
- O'Mahony — A separate Cork surname from Ó Mathghamhna, sharing only the personal name.[5][4]
Diaspora
The McMahons abroad
Emigration carried the name worldwide. In the 2010 United States census:
| Spelling | People | US rank |
|---|---|---|
| McMahon | 39,411 | 883rd |
| MacMahon | 554 | 39659th |
Source: US Census Bureau, 2010 surname file (public domain).
Heraldry
Is there a McMahon coat of arms?
There is no single McMahon coat of arms; Burke records several, each for a particular family. For Turlough MacMahon of Clonderlaw, registered as chief of his sept in 1472, he gives a silver shield with three red lions passing and looking back, and the motto 'Sic nos sic sacra tuemur', also allowed to Clare branches and to the French MacMahons. For the lords of Oriel he records a black ostrich on silver holding a gold horseshoe in its beak, with the mottoes 'So dorn dona dhubhfuiltibh' and 'Manus haec inimica tyrannis'.[7]
Websites selling a single “McMahon 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 McMahon
- Heber MacMahon (1600–1650) Bishop of Clogher who also served as a general in Ulster.
- Hugh MacMahon (1660–1737) Monaghan-born bishop of Clogher and archbishop of Armagh from 1715.
- Patrice de MacMahon (1808–1893) Marshal of France, Duke of Magenta and President of France from 1873 to 1879.
- Henry McMahon (1862–1949) British Indian Army officer and diplomat who gave his name to the McMahon Line.
- Ella MacMahon (1864–1956) Prolific Irish romance novelist.
- Brien McMahon (1903–1952) US senator for Connecticut and a leading figure in early atomic energy law.
- William McMahon (1908–1988) Prime minister of Australia from 1971 to 1972.
- Bryan MacMahon (1909–1998) Listowel playwright, novelist and short-story writer.
- Ed McMahon (1923–2009) American television announcer, game-show host and entertainer.
- Tony MacMahon (1939–2021) Clare button-accordion player and traditional music broadcaster.
- Jim McMahon (born 1959) American football quarterback who played fifteen NFL seasons, chiefly with the Chicago Bears.
Questions
Questions about the McMahon name
Is McMahon an Irish surname?
Yes. McMahon is the English form of the Gaelic Mac Mathghamhna, 'son of Mathghamhain'. Two separate Irish families took the name: the MacMahons of Corca Baiscinn in west Clare, who descended from the O'Briens, and the MacMahons who ruled Oriel, the kingdom that became Co. Monaghan. A smaller McMahon family in Fermanagh descended from the Maguires.[1][3]
What is McMahon in Irish?
The modern standard Irish form is Mac Mathúna. The older spelling, used by Woulfe and found in historical sources, is Mac Mathghamhna. Both mean 'son of Mathghamhain', a personal name meaning 'bear'.[4][1][2]
Are McMahon and MacMahon the same name?
Yes. Both are English spellings of Mac Mathghamhna, and Woulfe and Wikipedia treat them as one surname. The choice between Mc and Mac says nothing about whether a family came from the Clare or the Monaghan MacMahons; the home county is a far better guide.[1][2]
Are McMahon and O'Mahony related?
They share a personal name, Mathghamhain, but not a family. O'Mahony is from Ó Mathghamhna, a Cork family named from a Mathghamhain killed in 1014, while McMahon is from Mac Mathghamhna. Woulfe does note one overlap: an Ó Mathghamhna family in east Ulster came to be known as Mahon or MacMahon.[5][1]
How do you pronounce McMahon?
Wikipedia gives two common English pronunciations, 'mək-MAN' and 'mək-MAHN', with the stress on the second syllable and the h silent. Wiktionary records an Irish pronunciation that sounds the h, roughly 'mək-MA-hən'.[2][18]
Is there a McMahon family crest or coat of arms?
Not one for everyone named McMahon. Burke records arms for particular families: three red lions on silver for the MacMahons of Clonderlaw in Clare, later allowed to their branches and to the French MacMahons, and a black ostrich holding a horseshoe for the MacMahons of Oriel. A coat of arms belonged to the family it was recorded for.[7]
What is the McMahon clan motto?
Each family had its own. Burke gives 'Sic nos sic sacra tuemur' for the Clonderlaw MacMahons; Wikipedia translates it 'Thus we defend our sacred rights'. For the Oriel MacMahons he records the Irish 'So dorn dona dhubhfuiltibh', originally a battle cry with several suggested translations, and the Latin 'Manus haec inimica tyrannis'.[7][3]
Where in Ireland is the McMahon surname most common?
In the 1911 census the largest numbers of McMahons lived in Clare (2,967), Monaghan (1,003), Limerick (948). Relative to population, the name was most concentrated in Clare (284 per 10,000), Monaghan (140 per 10,000), Limerick (66 per 10,000).
How common was the McMahon surname in Ireland?
9,577 people were recorded as McMahon or MacMahon in the 1911 census of Ireland, making it the 63rd most common surname. That is roughly 0.2% of the population, or 1 person in 459.
Looking for a McMahon ancestor?
Search every McMahon household in the 1901, 1911 and 1926 censuses, with free images of the original forms.
Evidence
Sources
- Patrick Woulfe, Mac Mathghamhna, in Irish Names and Surnames (1923)
- Wikipedia, McMahon (surname) (2026)
- Wikipedia, McMahon clans (2026)
- Gaois research group, Dublin City University, Sloinnte: Irish surnames database (2022). Modern standard Irish forms.
- Patrick Woulfe, Ó Mathghamhna, in Irish Names and Surnames (1923)
- Wikipedia, Corcu Baiscind (2026)
- Sir Bernard Burke, The General Armory of England, Scotland, Ireland, and Wales (1884). Entries 'MacMahon (Lords of Oirghialla or Oriel)' and the 'Mac Mahon' entries for Clonderlaw, Coagy, Leadmore and the Duke of Magenta.
- Wikipedia, Carrigaholt (2026)
- Wikipedia, Patrice de MacMahon (2026)
- Wikipedia, Airgíalla (2026)
- Wikipedia, Farney (barony) (2026)
- Wikipedia, Heber MacMahon (2026)
- Wikipedia, Hugh MacMahon (2026)
- Wikipedia, Bernard MacMahon (bishop) (2026)
- Wikipedia, Clonderalaw (2026)
- Wikipedia, Moyarta (2026)
- Wikipedia, Dartree (2026)
- Wiktionary, McMahon (2026)
- 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.
How we compile these figures: methodology.