Ontonagon is one of the 83 counties in the state of Michigan. It was created in 1843 from parts of Chippewa and Mackinac counties as well as unorganized territory in the Upper Peninsula. As of the 2010 census, the population was 6,780. The county seat is Ontonagon. The county has 3,741 square miles in area, of which 1,311 square miles is land.