Sir John de Courcy (1150–1219) was an Anglo-Norman knight who arrived in Ireland in 1176. From then until his expulsion in 1204, he conquered a considerable territory, endowed religious establishments, built abbeys for both the Benedictines and the Cistercians and built strongholds at Dundrum Castle in County Down and Carrickfergus Castle in County Antrim.

Dundrum Castle, a ruin standing over the town of Dundrum, County Down, Northern Ireland. It was constructed by John de Courcy, sometime near the beginning of the 13th century, following his invasion of Ulster. The castle, built to control access into Lecale from the west and south, stands on the top of a rocky hill commanding fine views south over Dundrum Bay and the Mourne Mountains, the lands west towards Slieve Croob and the plains of Lecale to the east. The Castle is a State Care Historic Monument in the townland of Dundrum, in Newry, Mourne and Down District Council area, at grid ref: J4047 3700.