where is marion, illinois?
Marion, IL. Sponsored Topics. The city of Marion is the county seat of Williamson County, Illinois. The 2010 census counted 17,193 residents, making Marion the 25th most populated city outside of the Chicago Metropolitan Area, in Illinois, and the second most populous city in Southern Illinois, outside of the Metro-East, behind Carbondale.
Not to be confused with Marion, Illinois. Marion County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 39,437. Its county seat is Salem. Marion County comprises the Centralia, IL Micropolitan Statistical Area, which is included in the St. Louis-St.