Nenagh (nēˈnə, nēˈnăkh) [key], town (1991 pop. 5,825), Co. Tipperary, S central Republic of Ireland. It is an agricultural market with varied manufactures. Nenagh Castle (c.1200) has a circular keep. Nearby are ruins of a Franciscan friary, founded in the 13th cent. and destroyed by Oliver Cromwell's forces in 1650.