Wyandot County is a county located in the northwestern part of the U.S. state of Ohio. As of the 2020 census, the population was 21,900. Its county seat is Upper Sandusky. It was named for the Wyandot Indians, who lived here before and after European encounter. Their autonym is variously translated from their language as "around the plains" and "dwellers on the peninsula". The county was organized by the state legislature from parts of Crawford, Marion, Hardin and Hancock counties on February 3, 1845.