St. Louis County, Missouri, USA

St. Louis County is located in eastern Missouri, surrounding the independent city of St. Louis on the north, west and south and forming the largest population center within the Missouri portion of the St. Louis metropolitan area. Clayton serves as the county seat, while other major municipalities include Florissant, Chesterfield, University City, Maryland Heights, Kirkwood, Wildwood, Ballwin and Creve Coeur; large unincorporated areas also remain under direct county government. The Missouri River forms much of the county’s northern boundary, while the Mississippi River lies along its southeastern edge near Lemay and Oakville. The county ranges from densely developed inner-ring suburbs near St. Louis to employment centers, postwar suburbs, wooded hills and lower-density communities farther west. Interstates 44, 55, 64, 70, 170 and 270 provide the principal transportation corridors. St. Louis County covers 507.88 square miles of land and had 1,004,125 residents at the 2020 census, making it Missouri’s most populous county. The city of St. Louis is a separate county-equivalent jurisdiction and has not been part of St. Louis County since the two governments separated in 1876.