BRÉIFNE Brefni, Breffney, Breffny, Brenny.
Kingdom in western Ireland, formed by the mid-8th century on the borders of Connacht and Ulster by the powerful Connacht family of the Uí Briúin. Its power fell away but revived in the 12th and 13th centuries under the O’Rourkes (Ó Ruairc), who were descended from the Bréifne branch of the Uí Briúin. Their authority ceased to extend into southeastern Bréifne, where the family of the O’Reillys became predominant.
With the advance of English power in the 16th century eastern Bréifne became the larger part of the new county of Cavan, treated as part of Ulster, in 1579, while western Bréifne became the county of Leitrim (in Connacht) in 1585.
Bréifne belonged in the 12th century to a Bishopric of Kells that covered a wider area. As it became reduced in area the diocese became known as Tirbrunensis, a Latinised form of the Irish meaning land of the Uí Briúin.
With Bréifne split between the O’Rourkes and the O’Reillys, there were problems for the diocese and in 1453 the Pope decided that the cathedral should be in the small village of Kilmore on the borders between the contending families. In the Roman Catholic Church the diocese of Kilmore still covers the counties of Cavan and Leitrim, but in the Church of Ireland the diocese is more extensive as the dioceses of Ardagh and Elphin in eastern Connacht were united with it in 1839-41.