O'Reilly
O'Reilly (Ó Raghallaigh) is a common Irish surname. The O'Reillys were historically the kings of East Bréifne, a region that is now part of County Cavan in Ireland. They were part of the Uí Briúin Bréifne, a branch of the Connachta, and were closely related to the O'Rourkes of West Bréifne.
The name means "descendant of Raghallach" and is usually anglicised as O'Reilly, Reilly, or Riley. The Ó Raghallaigh family were part of the Connachta, and their eponym Raghallach is said to have died at the Battle of Clontarf in 1014.
O'Reilly is one of Ireland's most common surnames. It ranked around 10th or 11th in historical lists of common Irish names. The name is the patronymic form of Reilly.
In Gaelic Ireland, a self-styled O'Reilly clan chief once disputed the O'Rourke claim to the title Prince of Breifne. In 1994 the Chief Herald of Ireland recognized the O'Rourke as Prince of Breifne, and in 2003 the office stopped granting courtesy Gaelic titles.
Cadet branches of the O'Reillys include Brady, Vesey, and O'Reilly.
This page was last edited on 3 February 2026, at 18:52 (CET).