Roscommon, an unorganized county of N. Michigan, drained by the south branch of the Au Sable and some of the head waters of the Muskegon and Titibawasee rivers; area, 625 sq. m.; returned as having no population in 1870. It contains several lakes, the largest of which are Higgins's and Houghton's. The surface is rolling, and the soil poor.
Roscommon, a central county of Ireland, in Connaught, bordering on Sligo, Leitrim, Longford, Westmeath, King's, Galway, and Mayo; area, 915 sq. m.; pop. in 1871, 141,246. The Curlew and Braulieve mountains, which attain a height of from 1,000 to 1,200 ft., lie in the north of the county. The Shannon and its tributary the Suck flow on about two thirds of the whole boundary line, the former expanding in several lakes, of which the largest is Lough Ree. The Shannon has been made navigable by means of short canals, and the Suck can be ascended by flat-bottomed boats about 10 m. above its junction with the former. Grazing and agriculture are the chief occupations. Coarse woollen goods are made, and there are manufactories of tobacco pipes and earthenware. The principal towns are Roscommon, the capital, Boyle, and Elphin.