 Killeen was built as one of a pair of castles either side of a major roadway north, the other being the extant Dunsany Castle.Its estate was occupied continuously by the Cusack, and then after a marriage, Plunkett, families, from 1172 to 1951.The original structure at Killeen Castle is said to have been a Norman fortification, perhaps wooden, built for the de Lacy magnates, and held from 1172 by the Cusack family, beginning with Geoffrey de Cusack.