Osraige, also known as Osraighe or Ossory (modern Irish: Osraí), was a medieval Irish kingdom … In the early 12th century, dynastic infighting fragmented the kingdom, and it was re-adjoined to Leinster. The ancient Kingdom of the Osraige, an early Erainn tribe whose first king was Aengus Osrithe, flourished in the second century of the Christian era. In the fifth century the neighbouring tribe of the Deisi, aided by the Corca Laighde, conquered South Ossory, and for over a century, the Corca Laighde chiefs ruled in place of the dispossessed Ossory chiefs. Early in the seventh century the ancient chiefs recovered much of their lost possessions, the foreigners were overcome, and the descendants of Aengus ruled once more. One of the greatest was Carroll, prominent in the ninth century and distinguished in the Danish wars.
Kilkenny County forms much of what was known as the kingdom of Ossory. Kilkenny became one of the counties of Leinster in 1210, and also became the residence of Marshall, Earl of Pembroke, Strongbow’s heir and descendent, by whom Kilkenny Castle was built. Before the fourteenth century Marshall’s inheritance passed to the Butlers.