County Longford is a county in Ireland. It is in the province of Leinster. It is named after the town of Longford. Longford County Council is the local authority for the county. The population of the county was 46,634 at the 2022 census. The county is based on the historic Gaelic territory of Annaly (Anghaile), formerly known as Teffia (Teathbha).

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.