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This article is about the surname. For other uses, see O'Reilly (disambiguation).
Ó Raghallaigh
Country Kingdom of Connacht
Parent house Uí Briúin Bréifne
  • King of East Bréifne
  • King of Muintir Maelmórdha
  • Conde de O'Reilly
Founder Ragheallach mac Cathalan
Cadet branches Brady

O'Reilly (Irish: Ó Raghallaigh)[1] 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 Irish surnames.

It is also the patronymic form of the Irish name Reilly (Irish Gaelic: Uí Raghaile).[2] 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.

Naming conventions

Male Daughter Wife (Long) Wife (Short)
Ó Raghallaigh[3] 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 8th most common in 1890 and 11th in 1996.



People with the surname O'Reilly include:[4]


  • 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


Fictional people:

Other entities

See also


External links