O'Reilly
An Irish surname meaning “descendant of Reilly,” ultimately from a personal name associated with rallying or valour.
The #2,970 most common surname in the United States (2010 Census) — about 1 in every 25,571 Americans shares it.
Etymology
O'Reilly is the anglicized form of Irish Ó Raghallaigh, meaning “descendant of Raghallach.” The personal name Raghallach is usually explained as being related to a word for “valiant” or “sociable/rallying,” though the exact original sense is not perfectly certain. In English spelling, the Gaelic apostrophe is often dropped, producing forms like OReilly or Oreilly.
History
The Reilly name is strongly associated with County Cavan in Ireland, where the O’Reillys were a prominent Gaelic family and local rulers in medieval times. After the English-language spelling of Irish names became more common, O'Reilly and Reilly spread widely through Ireland and then overseas through emigration. The surname is now common in Ireland, Britain, North America, and Australia.
Origin
Regions
Variant spellings
Fun fact
The surname is so widely recognized that it has become a familiar brand name in the United States, especially in the tech and retail sectors.