County Monaghan is a county in Ireland. It is in the province of Ulster and is part of Border strategic planning area of the Northern and Western Region. It is named after the town of Monaghan. Monaghan County Council is the local authority for the county. The population of the county was 65,288 according to the 2022 census.

There are four provinces of Ireland: Connacht, Leinster, Munster and Ulster. The Irish word for this territorial division, cúige, meaning "fifth part", suggests that there were once five, and at times Meath has been considered to be the fifth province. In the medieval period, however, there were often more than five. The number of provinces and their delimitation fluctuated until 1610, when they were permanently set by the English administration of James I. The provinces of Ireland no longer serve administrative or political purposes but function as historical and cultural entities.