Osraige (Old Irish) or Osraighe (Classical Irish), Osraí (Modern Irish), anglicized as Ossory, was a medieval Irish kingdom comprising what is now County Kilkenny, western County Laois and parts of eastern County Tipperary, corresponding to the Diocese of Ossory. The home of the Osraige people, it existed from around the first century until the Norman invasion of Ireland in the 12th century. It was ruled by the Dál Birn dynasty, whose medieval descendants assumed the surname Mac Giolla Phádraig.
According to tradition, Osraige was founded by Óengus Osrithe in the 1st century and was originally within the province of Leinster. In the 5th century, the Corcu Loígde of Munster displaced the Dál Birn and brought Osraige under Munster's direct control. The Dál Birn returned to power in the 7th century, though Osraige remained nominally part of Munster until 859, when it achieved formal independence under the powerful king Cerball mac Dúnlainge. Osraige's rulers remained major players in Irish politics for the next three centuries, though they never vied for the High Kingship. In the early 12th century, dynastic infighting fragmented the kingdom, and it was re-adjoined to Leinster. The Normans under Strongbow invaded Ireland beginning in 1169, and most of Osraige collapsed under pressure from Norman leader William Marshal. The northern part of the kingdom, eventually known as Upper Ossory, survived intact under the hereditary lordship until the reign of King Henry VIII of England, when it was formally incorporated as a barony of the same name.
