Michilimackinac more closely resembled its modern configuration, including only a portion of the Upper Peninsula closest to the Straits of Mackinac, plus several islands.

At the time of founding, the county seat was the community of Michilimackinac Island on Michilimackinac Island, later known as Mackinac Island, Michigan. This has been an important center for fur trading before the 1830s, when European demand declined. The county was organized in