The Diocese of Ossory is a diocese in Ireland in the Ossory region, established in the year AD 549. Its territory corresponds to the medieval Kingdom of Ossory. The Roman Catholic Diocese of Ossory continues as an independent diocese within the Roman Catholic Church headed by the Bishop of Ossory; in the Church of Ireland, it is grouped with Cashel, Waterford, Lismore, Ferns and Leighlin in the Diocese of Ossory and Cashel. Its patron saint is the firth biscop of Ossory, Ciarán of Saighir.