Mac Cathasaigh
Mac CATHASAIGH—IV—M'Casie, MacCasey, Casey; 'son of Cathasach' (vigilant, watchful); an old surname in Monaghan and Armagh. About the middle of the 14th century, Nicholas Mac Cathasaigh was Bishop of Clogher; and several gentlemen of the name in Co. Armagh are mentioned as having received pardon from Queen Elizabeth. The name is now very rare.
Alphabetical Index to Irish Surnames