Monaghan (Mon'ahan), an inland county of Ulster, Ireland, between Tyrone on the N. and Meath (in Leinster) on the S. Its greatest length from north to south is 37 miles; the total area being 319,741 acres (496 sq. m.), of which about 140,000 are under tillage. Pop. (1841) 200,442; (1901) 74,611, of whom 54,757 were Catholics. The general surface is undulatory; the highest point is 1254 feet above the sea. Monaghan is interspersed with lakelets, and has many small streams. Limestone, freestone, and slates are worked. The flax crop has greatly increased of late years, and the linen manufacture is thriving. The principal towns are Monaghan, Carrick-macross, Clones, and Castle-Blayney. There are two county members. Monaghan possesses two round towers, at Clones and Inniskeen ; and there are several raths and Danish forts.
Monaghan (Gaelic Muinechan, 'Monkstown'), the county town, is 76 miles NNW. of Dublin by rail. It returned two members to the Irish parliament, and is the centre of some trade in agricultural produce. Pop. (1861) 3910; (1901) 2932. See Evelyn P. Shirley's History of the County of Monaghan (1877-80).