Comprises a large part of Derry and Tyrone counties, and part of Donegal; suffragan of Armagh. Saint Columba founded a monastery there between 546,562. The original abbey-church and the great church erected 1164 were demolished 1600. First bishop, probably Gervase O'Cervallen (c.1230); successors included Redmond O'Gallagher (1569) and Bernard O'Cahan (1683), from whom the succession continues unbroken to the present bishop, Bernard O'Kane (1926). See also: