O'Reilly

O'Reilly (Irish: Ó Raghallaigh) is a common Irish surname. The O'Reillys 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 common Irish surnames. It is also the patronymic form of the Irish name Reilly (Irish: Raghallach).