Roscommon County is a county located in the U.S. state of Michigan. As of the 2010 census, the population was 24,449. The county seat is Roscommon. The county was founded in 1840 and organized in 1875. Both the county and county seat are commonly referred to by locals as "Rosco".Roscommon is home to the Firemen's Memorial Festival which began is 1979 in honor of the fallen heroes. It is held on the third weekend in September, Thursday through Sunday.