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.

The Upper Peninsula of Michigan—also known as Upper Michigan or colloquially the U.P.—is the northern and more elevated of the two major landmasses that make up the U.S. state of Michigan; it is separated from the Lower Peninsula by the Straits of Mackinac. It is bounded primarily by Lake Superior to the north, separated from the Canadian province of Ontario at the east end by the St. Marys River, and flanked by Lake Huron and Lake Michigan along much of its south. Although the peninsula extends as a geographic feature into the state of Wisconsin, the state boundary follows the Montreal and Menominee rivers and a line connecting them.