Derg Castle, also called Castlederg Castle, is a post-medieval ruined fortification, situated on the north bank of the River Derg, within the town of Castlederg, in County Tyrone, Northern Ireland. It has given the town its name: 'Castlederg' derives from the Irish: Caisleán na Deirge, meaning 'Castle on the Derg'.
It is a Scheduled Historic Monument, administered by the Northern Ireland Department for Communities.[1]