Mackinac County is a county in the upper peninsula of the U.S. State of Michigan. As of the 2010 census, the population was 11,113. The county seat is sgt. ignance] The county was formerly known as Michilimackinac County, and it was created as one of the first counties of the Michigan Territory in 1818. According to the first Michigan Manual, by John T. Bois in 1838, the County contained 17,117,760 acres of the states total 38,732,800. In square miles, 27,688 of 57,022 as they figured. It contained most of the State north of Saginaw Bay, except Chippewa County which also was very large, 7,200 square miles, along the south shore of Lake Superior. The two comprised much more than half of the state in area.