Joliet (jōˈlēĕtˌ) [key], city (1990 pop. 76,836), seat of Will co., NE Ill., on the Des Plaines River; inc. 1857. It is a river port and an industrial shipping center, with limestone quarries and coal mines in the area, but riverboat casino gambling is now the city's primary industry. Machinery, electronic and transportation equipment, chemicals, and metal and paper products are made in Joliet, and there are oil refineries. Joliet is the seat of the College of St. Francis, and there are several state correctional facilites in or near the city.