==Geography==
St. Louis County is part of Missouri's easternmost tier of counties, facing the Mississippi River. It is largely river-bound, its northern border being formed by the Missouri River, most of its eastern border by the Mississippi (save the land boundary with the city of St. Louis), and most of its southern border by the Meramec River (though a small portion of the county lies south of the Meramec, including the city of Fenton). Only the western border is entirely on land. The county shares boundaries with St. Louis City and the state of [[Illinois]] to the east, [[Jefferson County, Missouri|Jefferson County]] to the south, [[Franklin County , Missouri|Franklin County]] to the west, and St. Charles County to the north and northwest. It has a total area of 523.02 square miles, including 507.8 of land and 15.22 of water.<ref>https://web.archive.org/web/20131021170230/http://www.census.gov/geo/maps-data/data/docs/gazetteer/counties_list_29.txt</ref>
St. Louis County lies at the extreme northeastern edge of the Ozark Highlands, and marks a transition from that region to the prairie and river floodplain of the middle Mississippi Valley. The southern and particularly southwestern portions are characterized by high, forested hills, and urban development here has been somewhat restricted, especially in the uplands between the Missouri and Meramec river bottoms. The highest point in the county, at about 900 feet above sea level, lies at the junction of Allenton and Hencken Roads in Wildwood, just northwest of the Six Flags St. Louis theme park. North of a line roughly paralleling Manchester Road (Missouri State Highway 100), the terrain becomes progressively less hilly, and the northernmost sections are characterized by flat, low-lying land, especially near the Missouri River's confluence with the Mississippi. Elevations drop to around 400 feet in places here and in the extreme southeastern corner, at the mouth of the Meramec.<ref>https://www.peakbagger.com/peak.aspx?pid=22281</ref>