Etymology
O'Reilly is a common Irish surname, an Anglicized form of the Gaelic Ó Raghailligh. The original Irish name means "descendant of Raghailligh", with Raghailligh being a personal name of unknown etymology. Variants include Reilly, Riley 2 and the unchanged Ó Raghailligh.
Historical background
The O'Reillys were historically the kings of East Bréifne, a kingdom in what is today County Cavan. They were part of the Connachta's Uí Briúin Bréifne kindred and closely related to the Ó Ruairc (O'Rourkes) of West Bréifne. According to tradition, the eponymous ancestor Raghallach died at the Battle of Clontarf in 1014. The name remained powerful through the Middle Ages in the region.
Distribution and frequency
O'Reilly is among the top ten most common surnames in Ireland, ranking 11th in census records from 1890 and 1997. The name is widespread throughout the island, reflecting its historical prominence and continued prevalence.
- Meaning: "Descendant of Raghailligh"
- Origin: Irish (Gaelic)
- Type: patronymic surname
- Usage regions: Primarily Ireland, plus diaspora in English-speaking countries
Variants
Sources: Wikipedia — O'Reilly