St. Louis County is located in eastern Missouri. It is bounded by the City of St. Louis and the Mississippi River to the east, the Missouri River to the north, and the Meramec River to the south. As of the 2020 census, the population was 1,004,125, making it the most populous county in Missouri, and was estimated to be 987,059 in 2023. The county is included in the St. Louis, MO–IL metropolitan statistical area.
After Great Britain took over former French territory east of the Mississippi River, many ethnic French colonists moved west. They settled the area of St. Louis County and founded the city of St. Louis in the late 1700s. The US acquired this territory in 1803 with the Louisiana Purchase.
In 1877 residents of the City of St. Louis voted to separate from the county and become an independent city. In the 1960s, with growing suburban development of Greater St. Louis, the county's population overtook that of the city for the first time. Restructuring of industry resulted in job and population declines in the city, and the county has continued to expand.
Through the decades, changing conditions have led many business and political leaders to propose merging the city and county as a single government. In 2019, efforts to put the issue to a statewide vote failed to get on a ballot.
History
Colonial settlement and early government
During the 18th century, several European colonial settlements were established in the area that would become St. Louis County. French colonists moved from east of the Mississippi River after France ceded territory to Great Britain after losing the Seven Years' War. It also ceded much of its territory west of the River to Spain.
St. Louis was founded by Pierre Laclède and Auguste Chouteau on February 14, 1764; they became major fur traders in the city. Founded in about 1767 was Carondelet, to the south. It was annexed by the city in 1871. During this time, the first governing body of St. Louis County was established (following the earlier Spanish governors).
This government, called the Court of Quarter Sessions, was composed of Charles Gratiot, Auguste Chouteau, Jacques Clamorgan, and David DeLaunay, all ethnic French or French Canadians; the court held judicial, executive, and legislative power. The first to gain municipal status in St. Louis County was St. Louis, which incorporated on November 9, 1809, under the territorial legislature. It gained city status on December 9, 1822. Leffingwell organized the town as a planned suburb (the first west of the Mississippi). Kirkwood was granted incorporation by the state in 1865. Among these were Chesterfield, which was settled in the 1820s in west St. Louis County. Gravois and Affton were settled in south St. Louis County in the 1850s and 1860s. In 1854, the School District of Maplewood was established. It included all of today's Maplewood district, part of what became Webster Groves, Missouri, along the south and southwest, a large part of St. Louis in the east, and to the north up to Clayton Road.
The first school in Florissant opened in 1819 under the direction of the Religious of the Sacred Heart, a Roman Catholic religious congregation. The instructor, Rose Philippine Duchesne, was a French immigrant who has been described as "one of the foremost educators in the state of Missouri". The earliest public school in Florissant was the St. Ferdinand School, which was authorized by the General Assembly in 1845 and operated until 1871 when the Florissant School District was formed.
Government changes and early courthouses
From 1813 to 1830, the county initiated several changes to its government. By an act of the territorial legislature, the Court of Quarter Sessions was succeeded by a panel of three judges of common pleas in 1813. The Court of Quarter Sessions held its first meeting in 1804 at a tavern in St. Louis, then regularly at a building at Third and Plum until 1817. Much of the dispute involved the double taxation of city residents and their proportionally lesser representation in county government. The reform of 1859, in which the County Court was abolished by the state government and replaced by a Board of Commissioners, was in large part a reaction to city outcry over mismanagement of tax money. This reform, however, pleased virtually no one pushing for reform, and it made little practical difference in the operation of the county government.
Postseparation political issues
The first meeting of the new County Court took place on January 22, 1877, at the home of James C. Sutton, in what is now Maplewood. The three judges appointed a new county clerk, sheriff, and treasurer. They also announced at that meeting that the new Court was functional (obviating the legal standing of the previous County Court, which continued to meet albeit without legal function until July 1877) and the transfer of all county buildings and property in the city of St. Louis to the city government. The Court continued to meet at the Sutton House in Maplewood until February 1877, when it convened at the Des Peres Grange Hall. It agreed then to rent space at the Mount Olive Hotel, in what is now University City, until deciding on a new location for the courthouse. The Court continued to meet at the Mount Olive Hotel from March 1877 to 1879. An additional four acres were given by M. F. Hanley, In October 1878 the courthouse donation and streets were platted in what would become the town of Clayton. Webster Groves incorporated in 1896, prompted by residents' demands for a police department after the murder of Bertram Atwater, a commercial artist from Chicago. Webster had earlier been settled in 1853 as a stop on the Missouri Pacific line.
Other incorporations before World War I included University City in 1906 near Washington University in St. Louis; Maplewood in 1908, also along the Missouri Pacific railroad line; Wellston in 1908 in the inner north county; Shrewsbury in 1913 east of Webster Groves; Clayton in 1913 south of University City; and Richmond Heights in 1913 south of Clayton. In the towns of Old Orchard and Webster Groves along the Missouri Pacific line, schools opened in 1867 and 1868, respectively. The first public schools in Kirkwood opened in 1866 as part of the newly formed Kirkwood School District; the district provided two years of high school from 1873 and opened a four-year Kirkwood High School in 1896.
Postwar
A new courthouse was built in Clayton in 1945 (it serves as the 21st-century County Police headquarters). The original 1878 courthouse was torn down in 1971 to be replaced by county government plaza and modern six-story courthouse. As part of a court-ordered desegregation plan, in 1975 the Ferguson-Florissant district annexed the Kinloch and the Berkeley school districts to combine the schools.
The county passed the city in population in the 1970 census when it had 951,353 compared to the city's 622,236. Industrial restructuring cost the city many jobs and residents. By the 2010 census, the city had fewer people than in the 19th century.
Geography
According to the United States Census Bureau, the county has a total area of , of which is land and (2.9%) is water.
Colloquially, St. Louis County is often divided into Mid, North, West, and South sections. North County lies north of Interstate 70, West County lies west of Interstate 270, South County lies south of Interstate 44 and Mid County lies in the middle of the three main bordering highways (I-70, I-270 & I-44) and the St. Louis county-city line.
Natural boundaries
The Missouri River forms the northern border with St. Charles County, exclusive of a few areas where the river has changed its course. The Meramec River forms most of its southern border with Jefferson County. To the east is the City of St. Louis and the Mississippi River. The western boundary with Franklin County is the north–south line where the distance between the Meramec and Missouri rivers is the shortest, bisecting the city of Pacific, roughly two blocks east of Hwy OO/F (First street).
Topography
The foothills of the Ozark Mountains begin in southwestern St. Louis County, with most of the rest of the county being a fairly level plateau. This western part of the county is the least developed, due to rugged topography. Bluffs along the Mississippi in the south of the county rise about 200–300 feet above the river. A major floodplain area is the Chesterfield Valley, in the western part of the county, along the Missouri River. It was formerly called "Gumbo Flats" after its rich, dark soil; it was submerged by at least ten feet of water during the Great Flood of 1993. The Corps of Engineers constructed a higher levee, and the county has permitted construction in the floodplain.
The Columbia Bottom is a floodplain in the northeast of the county at the confluence of the Mississippi and Missouri rivers; this is preserved as a conservation area open to the public. The Missouri Bottom area between the two other floodplains had been developed for agriculture, but it is being increasingly developed for residential, business, and industry. The River des Peres drains the interior of the county before flowing into constructed underground channels into the City of St. Louis. It was allowed to resurface, where it forms the boundary between southern portions of St. Louis City and St. Louis County. Other streams include Coldwater Creek, Bonhomme Creek, and Creve Coeur Creek, flowing into the Missouri River; Keifer Creek, Fishpot Creek, and Grand Glaize Creek, flowing into the Meramec River; Deer Creek and Gravois Creek, flowing into the River des Peres; and Maline Creek, flowing into the Mississippi River. The highest elevation is .
Geology
The bedrock is mainly limestone and dolomite, and much of the county near the rivers is karst terrain, with numerous caves, sinkholes, and springs. No igneous or metamorphic rock is exposed on the surface. A major outcropping of the St. Peter Sandstone formation, a fine white sandstone used for making clear glass, is mined in the southwest corner of the county in Pacific. Brick clay mining was once a major industry in the county. The Charbonier Bluff along the Missouri River is an outcropping of coal and was used a fueling station for steamboats. The "St. Louis Anticline", an underground formation, has small petroleum deposits in the north part of the county.
Flora and fauna
Before European settlement, the area was prairie and open parklike forest, maintained by Native Americans via burning. Trees are mainly oak, maple, and hickory, similar to the forests of the Ozarks; common understory trees include eastern redbud, serviceberry, and flowering dogwood. Riparian areas are heavily forested with mainly American sycamore. By the 1920s most of the timber in the county was harvested. Since that time, large parks and undeveloped areas in the western and southern parts of the county have grown dense forest cover. Old pastures are usually colonized with eastern red cedar. Most of the residential area of the county is planted with large native shade trees. In autumn, the changing color of the trees is notable. St. Louis County has the most recorded native species of plants in the state, but this is probably due to the intensive botanical research done in the area. Most species here are typical of the Eastern Woodland, but some southern species are found in swampland, and typical northern species survive in sheltered hollows. Invasive species, most notably Japanese honeysuckle, are common in some homesteads converted to parks; these are actively removed.
Large mammals include growing populations of whitetail deer and coyotes, which are becoming increasingly urbanized. Eastern gray squirrel, cottontail rabbit, and other rodents are abundant, as well as opossum, beaver, muskrat, raccoon, and skunk. Large bird species include wild turkey, Canada goose, mallard duck, various raptors like the turkey vulture and red-tailed hawk, as well as shorebirds, including the great egret and great blue heron. Winter populations of bald eagles are found by the Mississippi River around the Chain of Rocks Bridge. The county is on the Mississippi Flyway, used by migrating birds, and has a large variety of small bird species, common to the eastern U.S. The Eurasian tree sparrow, an introduced species, is limited in North America to the counties surrounding St. Louis.
Frogs are commonly found in the springtime, especially after extensive wet periods. Common species include American toad and species of chorus frogs, commonly called "spring peepers", that are found in nearly every pond. Some years have outbreaks of cicadas or ladybugs. Mosquitos and houseflies are common insect nuisances; because of this, windows are nearly universally fitted with screens, and "screened-in" porches are common in homes of the area. Populations of honeybees have sharply declined in recent years, and numerous species of pollinator insects have filled their ecological niche.
Climate
St. Louis County has a mix of a humid subtropical climate and a humid continental climate, with neither large mountains nor large bodies of water to moderate its temperature. The area is affected by both cold Canadian Arctic air, and also hot, humid air from the Gulf of Mexico. The county has four distinct seasons. Spring is the wettest season and produces erratic severe weather ranging from tornadoes to winter storms. Summers are hot, and the humidity can cause the heat index to rise to temperatures above . Fall is mild, with lower humidity and can produce intermittent bouts of heavy rainfall with the first snow flurries usually forming in late November. Winters are cool to cold with periodic snow and temperatures often below freezing. Winter storm systems, such as Alberta clippers, can bring days of heavy freezing rain, ice pellets, and snowfall.
The average annual temperature for the years 1971–2000, recorded at Lambert–St. Louis International Airport, is , and average precipitation is . The average high temperature in July is , and the average low temperature in January is , although these values are often exceeded. Temperatures of or below occur three days per year on average. The highest temperature ever recorded in St. Louis was , on July 14, 1954, while the lowest temperature on record is , on January 29, 1873.
Winter is the driest season, averaging about 6 inches of total precipitation. Springtime (March through May), is typically the wettest season, with under 10.5 inches. Dry spells of one or two weeks' duration are common during the growing seasons.
Thunderstorms can be expected on 40 to 50 days per year. A few of them will be severe with locally destructive winds and large hail, and occasionally accompanied by tornadoes. A period of unseasonably warm weather late in Autumn known as Indian summer is common—roses will still be in bloom as late as November or early December in some years.
Other geography
The largest natural lake in the county is Creve Coeur Lake. It was originally an oxbow of the nearby Missouri River and is now the centerpiece of a popular county park.
Manchester Road (Route 100) follows an ancient path westward out of St. Louis, following the boundary between the Missouri and Meramec watersheds. It is one of only two routes to leave the county without crossing any rivers (the other being State Highway T).
The Sinks is a karst area in the far northern part of the county, with numerous sinkholes.