Iosco County is a county located in the state of Michigan. As of the 2010 Census, the population was 25,887. The county seat is Tawas City.
In 1840 it was set off as Kanotin County, and renamed Iosco in 1843. The county was organized in 1857. Iosco is a Native American word meaning "water of light".
According to the U. S. Census Bureau, the county has a total area of 1,890 square miles (4,900 km2), of which 549 square miles (1,420 km2) is land and 1,341 square miles (3,470 km2) (71%) is water. The county is considered to be part of Northern Michigan.