County Roscommon (Irish: Contae Ros Comáin) is a county in the western region of the Republic of Ireland. It is also part of the province of Connacht. It is the 11th largest Irish county by area and 27th most populous. Its county town and largest town is Roscommon. Roscommon County Council is the local authority for the county. The population of the county is 64,065 according to the 2011 census.

Roscommon has the second least population density after Leitrim. It is the third largest of Connacht’s five counties by size and fourth largest in terms of population. The county borders every other Connacht county - Galway, Mayo, Sligo and Leitrim, as well as three Leinster counties - Longford, Westmeath and Offaly. In 2008, a news report said that statistically, Roscommon has the longest life expectancy of any county on the island of Ireland.

County Roscommon is named after the county town of Roscommon. Roscommon comes from the Irish Ros meaning a wooded, gentle height and Comán, the first abbot and bishop of Roscommon who founded the first monastery there in 550 AD.

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