Roscommon, an inland county of Connaught, Ireland, bounded E. by the Shannon, is 62 miles long from N. to S., by 35 from E. to W. Area, 607, 691 acres, of which barely one-fifth is under crops; more than one-half is permanent grass; one-sixth is waste. It belongs to the central plain of Ireland, but rises in the north into the Curlew (800 feet) and Braulieve (1377 feet) Mountains. Several lakes occur, as Allen, Boderg, and Ree, expansions of the Shannon, and Key, Gara, and Glinn in the north-west. The chief industry is the feeding, in the 'Plain of Boyle' and elsewhere, of sheep and cattle. The chief towns are Roscommon, Boyle, Castlerea, Elphin, and Strokestown. Pop. (1841) 254,551; (1861) 157,272; (1881) 132,490; (1901) 101,791 - 99,085 Roman Catholics. Roscommon returns two members. It possesses Celtic raths, remains of strong castles, and fine ecclesiastical ruins.