Mackinac County is a county in the Upper Peninsula of the U.S. state of Michigan. As of the 2020 census, the population was 10,834. The county seat is St. Ignace. Formerly known as Michilimackinac County, in 1818 it was one of the first counties of the Michigan Territory, as it had long been a center of French and British colonial fur trading, a Catholic church and Protestant mission, and associated settlement.