The family is of French origin, deriving its name from the French town of Cussac in Guyenne, in the Duchy of Aquitaine. At the time of the Anglo-Norman invasion of Ireland, Guyenne was part of the English King's dominions. Geoffrey de Cusack, the first of his name recorded in Ireland, came from Guyenne, France to Ireland at the invitation of Hugh de Lacy, Lord of Meath to help colonize Meath about the year 1175. He held land there under his relative, Adam de Feipo, Baron of Skreen, county Meath, who in turn held them from de Lacy. He appears as witness to a charter which can be dated before 1190. Geoffrey was lord of the manor of Killeen, which comprised 3,346 acres in county Meath. Geoffrey made several grants to religious houses about this time and he granted four crannocks of corn from the Killeen lands to the Hospitallers of Dublin for the good of the souls of his wife, his ancestors, his successors and himself. He also granted 40 acres of arable land in the Barony of Killeen to the Priory of Llanthony Prima in Monmouthshire for the welfare of himself and his wife, and for the repose of the souls of his brother, Richard, and his overlord, Adam de Feipo.9