Mayo, a maritime county of the Irish province of Connaught, is bounded by the Atlantic, Sligo, Roscommon, and Galway. Area, 1,360,731 acres, of which nearly 26 per cent. is bog and 18 per cent. barren ; pop. (1841) 388,887; (1901) 199,166, of whom 213,602 were Catholics. The eastern half of the county is more or less a plain, the western half mountainous, the highest points being Muilrea (2688 feet), Nephin (2530), and Croagh Patrick (2370). Ironstone abounds, but is not worked; there are several valuable slate-quarries. The chief towns are Castlebar, West-port, Ballina, and Ballinrobe. The coast-line is about 250 miles, and is indented by Killala, Blacksod, and Clew Bays, Killary Harbour, and Broad Haven. Off Mayo, too, lie the islands Achil (35,283 acres), Clare (3959), etc. Loughs Mask and Corrib lie on the southern border, and Loughs Conn, Castlebar, Cullen, Carragh, Corra-niore within the county. A valuable salmon-fishery exists in the river Moy, and Lough Mask is the home of the ' gillaroo ' trout. Four members are returned. The antiquities are chiefly ecclesiastical - four round towers, and at Cong a splendid ruined abbey of the 12th c.