Sandusky County is a county located in the northwestern part of the U.S. state of Ohio. As of the 2020 census, the population was 58,896. Its county seat and largest city is Fremont. The county was formed on February 12, 1820, from portions of Huron County. The name is derived from the Wyandot word meaning "water". The Sandusky River runs diagonally northeast through the county to its mouth on Sandusky Bay, opening into Lake Erie.