Costello (barony)

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Costello^[1] is one of the ancient baronies of Ireland. Unusually for an Irish barony, it straddles two counties: County Mayo and County Roscommon. It comprises the modern day districts of Kilkelly, Kilmovee, Killeagh, Kilcolman, and Castlemore.

Prior to the Norman conquest of Ireland, the area was called Sliabh Lugha and was ruled by the Ó Gadhra dynasty. In the 12th century, Milo de Angelo removed the O'Gadhra seat from Airtech Mór to Costello. He built a castle there, known as Castlemore. The Ó Céirín (Kearns) family also had a presence as lords of Ciarraige Locha na nÁirne.