O'Reilly (Irish: Ó Raghallaigh) is a group of families, ultimately all of Irish Gaelic origin, who were historically the kings of East Bréifne in what is today County Cavan. The clan were part of the Connachta's Uí Briúin Bréifne kindred and were closely related to the Ó Ruairc (O'Rourkes) of West Bréifne. O'Reilly is ranked tenth in the top twenty list of most commom Irish surnames.
|Parent house||Uí Briúin Bréifne|
|Country||Kingdom of Connacht|
|Founder||Ragheallach mac Cathalan|
|Current head||Myles Hugh O'Reilly|
|Final ruler||Maelmordha O'Reilly|
It is also the patronymic form of the Irish name Reilly (Irish Gaelic: Uí Raghaile). It is commonly found throughout Ireland, with the greatest concentration of the surname found in County Cavan followed by Longford, Meath, Westmeath, Fermanagh and Monaghan, and the Province of Leinster.
|Male||Daughter||Wife (Long)||Wife (Short)|
|Ó Raghallaigh||Ní Raghallaigh||Bean Uí Raghallaigh||Uí Raghallaigh|
It is usually anglicised as Reilly, Riley and O'Reilly. The original form of the name, Ó Raghallaigh, denotes "from/of Raghallach", the name Raghallach thought to be derived from the compounds ragh (meaning "race") and ceallach (meaning "sociable").
The Ó Raghallaigh family were part of the Connachta, with the eponymous Raghallach said to have died at the Battle of Clontarf in 1014. The family became the kings of East Breifne, modern-day County Cavan and County Longford.
The name is common and widespread throughout Ireland, ranked 11th most common in 1890 and in 1997.
The O'Reilly Clan Chieftain to this day is at odds with the O'Rourke Clan Chieftain because both clans viciously contest each other for the title Prince of Breifne. This was settled in 1994 when the Chief Herald of Ireland made the O'Rourke Chief the Prince of Breifne, but the Office of the Chief Herald stopped granting courtesy titles to Gaelic Chiefs in 2003 (see O'Rourke). In 2017, with the election of the new O'Reilly Chief, the rivalry has been rekindled.
People with the surname O'Reilly include:
- Alejandro O'Reilly (1722–1794), second Spanish governor of colonial Louisiana
- Andreas O'Reilly (1742–1832), Irish-born Austrian general
- Bernard O'Reilly (1903–1975), located the wreck of a Stinson aircraft in the McPherson Range, Australia, 1937
- Bernard O'Reilly (bishop of Hartford) (1803–1856), Roman Catholic bishop
- Bernard O'Reilly (bishop of Liverpool) (1824–1894), Roman Catholic bishop
- Bill O'Reilly (1949–), American commentator and television show host of The O'Reilly Factor on the Fox News Channel
- Bill O'Reilly, Australian cricketer
- Bob O'Reilly, Australian rugby league footballer
- Caitriona O'Reilly, poet and critic
- Cal O'Reilly, Canadian ice hockey player
- Cameron O'Reilly, Irish and Australian businessman
- Cassia O'Reilly, Irish singer-songwriter
- Charles O'Reilly (died 1800), Roman Catholic Bishop of Kilmore from 1798 to 1800.
- Danny O'Reilly, Lead singer of Irish band, The Coronas
- David O'Reilly, several people including
- David O'Reilly, film director and artist
- David J. O'Reilly, Chairman and CEO of Chevron Corporation
- Dermot O'Reilly (1942–2007), Singer and songwriter in band Ryan's Fancy, contributed strongly to the Music of Newfoundland and Labrador.
- Des O'Reilly (1954–2016), Australian rugby league player
- Emily O'Reilly, Irish journalist
- Emma O'Reilly, Irish physiotherapist and cycling soigneur, bullied and sued by Lance Armstrong.
- Finbarr O'Reilly, Canadian photographer
- Gary O'Reilly, English footballer
- Genevieve O'Reilly, Irish actress
- Heather O'Reilly (1985–), American soccer player
- Hugh Reily (1630–1695), Irish M.P. and political author
- James Reilly (Canadian politician) (1835–1909), Canadian businessman and politician from Alberta
- James O'Reilly, American Roman Catholic priest
- John Reyly (recte O'Reilly) (c.1646 – 17 February 1717) was an M.P. for Cavan County (Parliament of Ireland constituency) in the Parliament of Ireland of 1689, known as the Patriot Parliament.
- John O'Reilly (1940–), Canadian politician from Ontario
- Joseph O'Reilly, Irish politician
- Kyle O'Reilly (1987–), ring name of Canadian professional wrestler Kyle Greenwood
- Leonora O'Reilly, an American feminist
- Luke O'Reilly (disambiguation)
- Mary Margaret O'Reilly, Assistant Director of the United States Bureau of the Mint from 1924 to 1938
- Margaret M. O'Reilly (1962– ), Irish-born, American art curator, New Jersey State Museum
- Matthew O'Reilly, Irish politician and farmer
- O'Reilly, Lords of Bréifne (c. 1161–1607)
- Patrick Thomas O'Reilly (1833-1892), U.S. Catholic bishop, born in Ireland
- Peter O'Reilly (civil servant) (1827–1905), settler and official in the Colony of British Columbia
- Peter O'Reilly (hurler) (1902–1940), Irish hurler
- Philip O'Reilly (c.1600–1655), M.P. for County Cavan
- Philip Og O'Reilly (c. 1640–1703) was an M.P. for Cavan Borough in the Parliament of Ireland of 1689, known as the Patriot Parliament.
- Philip Reyley (recte O'Reilly) (b. c.1630 – d. after 1689) was an M.P. for Cavan County (Parliament of Ireland constituency) in the Parliament of Ireland of 1689, known as the Patriot Parliament.
- Randall C. O'Reilly (1967–), professor of psychology, developer of Leabra
- Robert O'Reilly (1950–), American actor
- Ruth O'Reilly (born 1981), Irish rugby union player
- Ryan O'Reilly (ice hockey) (1991–), Canadian ice hockey player
- Ryan O'Reilly (wrestler) (1980–), American professional wrestler
- Samuel O'Reilly (19th century), American inventor
- Stephen O'Reilly (1964–) (better known as Stephen Egerton), American musician
- Stephen O'Reilly, American actor
- Stephen O'Reilly, Australian footballer
- Terry O'Reilly, hockey player
- Tom O'Reilly (1915–1995), Irish Fianna Fáil politician
- Tim O'Reilly (1954–), founder of O'Reilly Media
- Tom O'Reilly (1915–1995), Irish Gaelic footballer and politician
- Tom O'Reilly Irish Sinn Féin politician
- Tom O'Reilly, Papua New Guinea international
- Tony O'Reilly (1936–), Irish businessman
- Valli O'Reilly, Makeup artist
- Walter Cresswell O'Reilly (1877–1954), Australian Commonwealth Film Censor and founding President of the National Trust of Australia
- Christopher O'Riley (born 1956), American classical pianist and public radio show host
- Don O'Riley (1945–1997), Major League Baseball pitcher
- Bunny Wailer (born 1947), reggae musician sometimes known as Bunny O'Riley
- Jon Riley (1824–1879), US army deserter also known as John O'Riley
- Mr. O'Reilly, Fictitious Irish character/builder portrayed by the Irish actor David Kelly on the episode "The Builders" from Fawlty Towers
- Aloysius Umbongo N'Danga O'Reilly, fictitious character in the song "Baguette Dilemma for the Booker Prize Guy" by the band Half Man Half Biscuit on their 2014 album Urge for Offal
- Corporal Walter "Radar" O'Reilly, character in the M*A*S*H media franchise
- O'Reilly Auto Parts, an American chain of automotive supply stores
- O'Reilly Media (formerly O'Reilly & Associates), an American media company
- Baba O'Riley, a song by The Who
- Information on the last name O'Reilly
- Information on the last name O'Reilly (2)
- "Ó Raghallaigh". Sloinne. 5 December 2015.
- Matheson, Robert E. (1894), Special report on surnames in Ireland, with notes as to numerical strength, derivation, ethnology, and distribution; based on information extracted from the indexes of the General register office. Appendix to the Twenty-Ninth Detailed Annual Report of the Registrar-General of Marriages, Births, and Deaths in Ireland, Dublin: For Her Majesty's Stationary Office by Alexander Thom & Co. (Limited), p. 9 (accessible online)
- Murphy, Sean J. (2014), A Survey of Irish Surnames 1992–97. In: Studies in Irish Genealogy and Heraldry, Windgates, County Wicklow, pp. 14–29 (first published 2008, last revision 2014), here p. 27 (accessible online)
- "O'Reilly coat of arms, family crest and O'Reilly family history". irishsurnames.com. Retrieved 1 January 2008.
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