Edwardsville is a city in Madison County, Illinois, United States, and its county seat. The population was 26,808 as of the 2020 census. The …Edwardsville is a city in Madison County, Illinois, United States, and its county seat. The population was 26,808 as of the 2020 census. The city was named in honor of Ninian Edwards, former governor of the Illinois Territory. Edwardsville is a part of Southern Illinois and the Metro East region within Greater St. Louis, located 18 miles northeast of downtown St. Louis.