St. Charles County, Missouri

St. Charles County is located in the central eastern part of the U.S. state of Missouri. As of the 2020 census, the population was 405,262, making it Missouri's third-most populous county. Its county seat is St. Charles. The county was organized October 1, 1812, and named for Saint Charles Borromeo, an Italian cardinal.

St. Charles County is part of the St. Louis, MO-ILMetropolitan Statistical Area and contains many of the city's northwestern suburbs. The wealthiest county in Missouri, St. Charles County is one of the nation's fastest-growing counties.

St. Charles County includes a part of the Augusta AVA, an area of vineyards and wineries designated by the federal government in 1980 as the first American Viticultural Area. The county's rural outer edge along the south-facing bluffs above the Missouri River, is also part of the broader Missouri Rhineland.