Comprises Monaghan, nearly all of Fermanagh, a large portion of Tyrone, and portions of Donegal, Louth, and Cavan. Suffragan of the archdiocese of Armagh. Founded by Saint Patrick in 454. Notable bishops includeSee also:
- Saint Macarten, first bishop
- Saint Aidan of Lindesfarne
- Heber MacMahon (1643-1650) who figured prominently in the war of the Irish Confederates
New Catholic Dictionary