Mayo is a maritime county of northwest Ireland in Connaught Province Province, bounded on the east by Sligo and Roscommon, on the south by County Galway and Galway Bay, and on the west and north by the Atlantic Ocean. Its ara is 2156 square miles.
The coast line is wild and irregular, broken by many bays and coves, the mostimportnat being Killary and Broad Haven harbors, and Clew, Killala, Blacksod, Tullaghan, Cluggin, Bertraghboy, Kilkieran, Mannin, and Ballyconnealy bays. The surface of the county is flat and slightly undulating in the east. On the northwest and southwest rise the Nephin Beg and partry ranges. In the northeast are the Gamph Mountains. Mayo has more lakes than any other Irish county. Lough Conn, in the east central part, is the largest lake wholly within the county. Off the shores of Mayo are hundreds of islands.
Castlebar is the county town. Other towns are Keep, Melmillet, Bally-Castle. On Clare Island is one of the castle strongholds of Grace O'Malley.