Are of Cambro (Welsh)-Norman descent from the family of
(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.
Thanks to Bob Costello for
providing the above information.