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. It's part of a dispersed urban area that developed out of the early 20th Century coal fields. Today Marion serves as the largest retail trade center in Southern Illinois with its central location along Interstate 57 and Illinois Route 13 (colloquially known as Southern Illinois' "Main Street"). It's home to the Illinois Star Centre mall and the Southern Illinois Miners baseball team, and is in the process of being selected for Illinois' first STAR Bonds District for the proposed Millennium Development.
The city is part of the Marion-Herrin Micropolitan Area and is a part of the Carbondale-Marion-Herrin, Illinois Combined Statistical Area with 123,272 residents, the sixth most populous Combined statistical area in Illinois. The city is also part of the unofficial Metro Lakeland area.
Following the creation of Williamson County out of the south half of Franklin County by the Illinois General Assembly, three commissioners appointed by the lawmakers met at Bainbridge, Illinois, on August 19, 1839, for the purpose of locating a new county seat as close to the center of the county as possible. The next day, August 20, they laid out a town of 20 acres (81,000 m2) with a public square about one-quarter of a mile east of the county's center, but a point on top of a slight hill of 448 feet (137 m) above sea level. The site sat in a small open grassland known as Poor Prairie. For a name, they chose Marion to honor American Revolutionary War hero General Francis "Swamp Fox" Marion.