Casserly, Costelloe, Mac Coistealbh, Mac Costello, Nangle
The Costello name, and its variations, are of Anglo Norman origins, and have an interesting history. The original name of the clan was deAngulo, or Nangle, and it became Costello as the family were absorbed into the Gaelic tradition. They took the name of one of their forebearers, Jocelyn, which was Gaelicised to Goisdealbh, to become Mac Goisdealbhaigh. This name was subsequently given the English Costello. The family stronghold was in Mayo, where the barony of Costello was named after them, and the surname today is widely dispersed across the country.