Leitrim, a N. W. county of Ireland, in the province of Connaught, bordering on Donegal bay and the counties Donegal, Fermanagh, Ca-van, Longford, Roscommon, and Sligo; area, 613 sq. m.; pop. in 1871, 95,324. Lough Allen divides it into two very nearly equal parts, that lying S. being chiefly an undulating plain, bounded W. by the Shannon, and that lying N. hilly with intermediate valleys traversed by fertilizing streams. Loughs Macnean (4 by 2 m.) and Melvin (8 by 2 m.) separate the N. E. part of the county from Fermanagh, and the river Duff separates it from Sligo. The coast for the most part is a rocky bluff rising above a rough stony beach, and exposed to the whole swell of the Atlantic. It has no port or harbor; there are salmon fisheries at the mouths of the rivers. The principal streams are the Shannon, Rinn, and Bonnet. The surface is diversified, and in the valleys and plains the soil is extremely fertile. Near Lough Allen is an extensive coal formation. Lead, copper, and manganese are found. The climate is raw and damp, but more genial in the south than in the north. The principal crops are potatoes, oats, and hay; the county generally is more adapted to grazing than tillage. The manufactures are linens and woollens for domestic use, and coarse pottery.

The principal towns are Carrick-on-Shannon (the county town), Manor Hamilton, and Mohill.