The Clan/Sept History

Are of Cambro (Welsh)-Norman descent from the family of Gilbert deAngulo (later: Gilbert N'angle), who participated in the Norman invasion of Ireland (1167-1172AD) with Richard deClare (Strongbow), Gilbert had two sons: Jocelyn and Costilo, and the son of the latter, known as MacOisdealbh (Gaelic for Son of Costilo) participated in the Norman invasion of Connaught in 1235, along with the deBurgos (Burkes) and the deLacys. He established the Barony of MacOisdealbh (later: MacCostello) in eastern Mayo & western Rosscommon, which lasted some 400 years. The Costellos were the first of the great Norman families in Ireland to use the "Mac" (Son of) prefix to their name. Like many other Cambro-Norman families they became "More Irish than the Irish themselves". The Barony of MacCostello is still an identifiable geopolitical district in Mayo to this day, and the Costello name is very common in Mayo.