Tuscola is a city and the county seat of Douglas County, Illinois, United States. The population was 4,636 at the 2020 census. The city of Tus…Tuscola is a city and the county seat of Douglas County, Illinois, United States. The population was 4,636 at the 2020 census. The city of Tuscola;s name came from an unknown Native American tribe's word for "flat plain."