Saint Charles is a city in, and the county seat of, St. Charles County, Missouri, United States. The population was 65,794 at the 2010 census, making St. Charles the ninth-largest city in Missouri. Situated on the Missouri River, St. Charles, Missouri is a northwestern suburb of St. Louis. Founded circa 1769 as Les Petites Côtes, or "The Little Hills" in French, by Louis Blanchette, a French-Canadian fur trader, when the area was nominally ruled by Spain following the Seven Years' War, St. Charles is the third-oldest city in Missouri.