Ó Raghailligh is an Irish surname meaning "descendant of Raghailligh." The given name Raghailligh, from which the surname derives, is of uncertain etymology. This surname is closely related to the more common anglicized forms O'Reilly and Reilly, which are widely used in Ireland and among the Irish diaspora. The form Riley 2 is also a variant, though it may sometimes overlap with the English Riley derived from a place name.
Historically, the Ó Raghailligh family were a notable Gaelic Irish clan, the Uí Raghallaigh. They were based in County Cavan and parts of surrounding counties, forming the kingdom of East Bréifne. The name is famously connected to the O'Reillys, a powerful sept that controlled this territory for centuries. The original form Ó Raghailligh reflects the native Irish patronymic, while O'Reilly is its most common anglicized spelling, with variations dating back to the earliest written records.
- Meaning: Descendant of Raghailligh (original given name of unknown meaning)
- Origin: Irish
- Type: Patronymic surname
- Usage: Predominantly Irish, Ó Raghailligh specifically indicates affiliation with the Uí Raghallaigh kin group
Sources: Forebears — Ó-raghailligh