Includes nearly all Longford, greater portion of Leitrim, and parts of Offaly, Westmeath, Roscommon, Cavan, and Sligo counties; established in the 5th century; suffragan of Armagh. Saint Patrick consecrated the first bishop, Saint Mel. Several of the O'Feral clan occupied the see, 14th and 15th centuries. Under Bishop Flynn, 1729, the Diocese of Clonmacnois, seat of the famous ancient abbey and school, was united with it.