Saint Charles. 1 City (1990 pop. 22,501), Kane co., NE Ill., on the Fox River, a suburb of Chicago; inc. 1850. Located in an agricultural area (corn and soybeans), the city has food-processing, aluminum and plastic products, and communications equipment industries. 2 City (1990 pop. 54,555), seat of St. Charles co., E Mo., on the low bluffs along the north bank of the Missouri River, a suburb of St. Louis; settled by French traders 1769, inc. as a city 1849. Its manufactures include clothing, shoes, metal products, electronic and computer equipment, and wood cabinets. St. Charles began as an important trading post, and the city served as the state capital from 1821 to 1826. Lindenwood Univ. and the Sacred Heart Convent (1818) are there. Of interest are historic Main Street and the old capitol building.