County Roscommon (Irish: Contae Ros Comáin) is a county located in central Ireland. Area: 2547 km² (983 square miles). Roscommon is in the province of Connacht.

It is the only county in Connacht (or Connaught) that does not have a sea shore. Roscommon is also the name of the county town. Athlone, on the River Shannon, which lies partly in Roscommon and partly in County Westmeath (in the neighbouring province of Leinster), is considered to be Ireland's most central town.

Tulsk is the nearest village to the mythological site of Rath Cruachán, home of Queen Medb (Maebh, Maeve) and the Morrigan, which was the starting point for an epic tale in Irish Literature of the Táin Bó Cúailgne, or Cattle Raid of Cooley, famously translated by Thomas Kinsella.

Roscommon has much to interest those interested in Irish heritage or history. Lough Key in north Roscommon is noted for having thirty-two islands. This is, coincidentally, the number of counties on the island of Ireland.

County Roscommon has been twinned with Castle Point in Essex, England since April 1998.