Marion is a city in Williamson County, Illinois, United States. The population was 16,035 at the 2000 census. A census update in 2007 found the population to be 17,011. It is the county seat of Williamson County. Marion was named for Francis Marion, the 'Swamp Fox' in the Revolutionary War. The County's namesake, Hugh Williamson served as a physician in the same campaign. It is also the home to the first supermax prison in the U.S., United States Penitentiary Marion. Marion's slogan is 'Marion: Hub of the Universe.' The most recognizable feature of Marion is the clock tower in the center of the city square that replaced the court house. The tallest building in Marion is First Baptist Church of Marion, with a steeple reaching a height of approximately 105 feet. Marion apartments for rent comparison page shows most up to date rent information on Marion apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.