Monaghan, an inland county of Ireland, in the province of Ulster, bordering on Tyrone, Armagh, Louth, Meath, Cavan, and Fermanagh; area, 498 sq. m.; pop. in 1871, 112,785. The. surface is in general hilly, except in the S. E., which is level, and forms the northern limit of the great central plain of Ireland. The principal mountains are the Slieve Beagh range, whose highest summit is 1,254 ft. above the sea. The chief rivers are the Blackwater, Fane Glyde, and Finn. There are several hikes the largest being Muckno, or Barrac Lough, which is about 3 m. long and 1 m. broad. The soil is moory and peaty in the elevated districts, but fertile in the central and southern. The staple manufactures are linen, woollen, and earthenware. The minerals are iron, lead, coal, slate, marble, and building stone. The chief towns are Monaghan, the capital (pop. about 4,000), Clones, Castle Blay-nev, and Carrickmacross. It is traversed by the Ulster canal and various lines of railway. The county was a part of the grant made by Henry II. to De Courcy, was recaptured by the native chiefs, and in the reign of Elizabeth was erected into a shire.