Coordinates: 54°14′38″N 7°02′24″W / 54.244°N 7.040°W / 54.244; -7.040

County Monaghan ( /ˈmɒnəhən/; Irish: Contae Mhuineacháin) is a county in Ireland. It is part of the Border Region and is also located in the province of Ulster. It is named after the town of Monaghan. Monaghan County Council is the local authority for the county. The population of the county is 60,495 according to the 2011 census.

Monaghan is the fourth smallest of the Republic's 26 counties in area and fourth smallest by population. It is the second smallest of Ulster’s nine counties in size and smallest in terms of population.

Notable mountains include Mullyash Mountain, Slieve Beagh (on the border with Tyrone and Fermanagh) and Coolberrin Hill (214 m, 702 ft). Lakes include Lough Egish, Lough Fea, Muckno Lough, Lough Avaghon, Inner Lough (in Dartrey Forest), Drumlona Lough, White Lough and Emy Lough. Rivers in Monaghan include the River Fane (along the Louth border), the River Glyde (along the Louth and Meath borders), the Ulster Blackwater (along the border with County Tyrone) and the Dromore river (along the border of County Cavan, linking Cootehill to Ballybay).

Monaghan (Irish: Muineachán) is the county town of County Monaghan, Ireland. Its population at the 2011 census was 7,452 including suburbs and environs. The town is on the N2 road from Dublin to Derry and Letterkenny.

The toponym Muineachán derives from a diminutive plural form of the Irish word muine meaning "brake" (a thickly overgrown area) or sometimes "hillock". The county council's preferred interpretation is "land of the little hills", a reference to the numerous drumlins in the area. Another translation of the name splits the Irish name into "Muine Acháin" - with "acháin" meaning field. With this separation, and depending on the interpretation of "muine", "Muine Acháin" could be translated to "bushy (over-grown) field" or "hilly field".

The coat of arms of Monaghan town features a red hand on a shield on a tower. It has been speculated that the red hand here is the hand of the O'Neill family since the Battle of Clontibret between the forces of Hugh O'Neill and the English Crown was fought in northern Monaghan in May 1595.