Jefferson County is located in the eastern portion of the U.S. state of Missouri. It is a part of the St. Louis Metropolitan Area. As of the 2020 census, the population was 226,739, making it the sixth-most populous county in Missouri. Its county seat is Hillsboro. The county was organized in 1818 and named in honor of former president Thomas Jefferson. In 1980, according to the U.S. census held that year, the county contained the mean center of U.S. population. Notably, this was the first census in which the center of population was west of the Mississippi River. Jefferson County is part of the St. Louis Metropolitan Statistical Area and encompasses many of the city's southern suburbs.
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👉 Jefferson County, Missouri in the context of Greater St. Louis
Greater St. Louis is the 23rd-largest metropolitan statistical area (MSA) in the United States consisting with an MSA population more than 2.8 million, and almost 3 million CSA the largest in Missouri, and the second-largest in Illinois. Its core city—St. Louis, Missouri—sits in the geographic center of the metro area, on the west bank of the Mississippi River. The river bisects the metro area geographically between Illinois and Missouri, although the latter portion is much more populous. The MSA includes St. Louis County, which is independent of the City of St. Louis; their two populations are generally tabulated separately.
The St. Louis, MO-IL metropolitan statistical area (MSA) includes the City of St. Louis; the Illinois counties of Bond, Calhoun, Clinton, Jersey, Macoupin, Madison, Monroe, and St. Clair (known collectively as the Metro East); and the Missouri counties of Crawford (only the City of Sullivan), Franklin, Jefferson, Lincoln, St. Charles, St. Louis (separate from and not inclusive of the city of St. Louis), and Warren.
In this Dossier
- ⭐ Core Definition: Jefferson County, Missouri
- 👉 Jefferson County, Missouri in the context of Greater St. Louis
- Jefferson County, Missouri in the context of Meramec River
- Jefferson County, Missouri in the context of Herculaneum, Missouri
- Jefferson County, Missouri in the context of Hillsboro, Missouri
- Jefferson County, Missouri in the context of Arnold, Missouri
Jefferson County, Missouri in the context of Meramec River
The Meramec River (/ˈmɛrɪmæk/), sometimes spelled Maramec River (the original US mapping spelled it Maramec but later changed it to Meramec), is one of the longest free-flowing waterways in the U.S. state of Missouri, draining 3,980 square miles (10,300 km) while wandering 218 miles (351 km) from headwaters southeast of Salem to where it empties into the Mississippi River near St. Louis at Arnold and Oakville. The Meramec watershed coverssix Missouri Ozark Highland counties—Dent, Phelps, Crawford, Franklin, Jefferson, and St. Louis—and portions of eight others—Maries, Gasconade, Iron, Washington, Reynolds, St. Francois, Ste. Genevieve, and Texas. Between its source and its mouth, it falls 1,025 feet (312 m). Year-round navigability begins above Maramec Spring, just south of St. James. The Meramec's size increases at the confluence of the Dry Fork, and its navigability continues until the river enters the Mississippi at Arnold, Missouri.
Jefferson County, Missouri in the context of Herculaneum, Missouri
Herculaneum is a city in Jefferson County, Missouri, and is a suburb of St. Louis. The population was 4,273 at the 2020 United States census. The City of Herculaneum was the first county seat of Jefferson County from January 1, 1819, to 1839. The city celebrated its bicentennial throughout 2008.
The city received the "Tree City USA" designation by the Arbor Day Foundation for 11 consecutive years, 2007 through 2017. The city is the honorary hometown of the 40th Airlift Squadron, "The Screaming Eagles," from Dyess Air Force Base in Texas.
Jefferson County, Missouri in the context of Hillsboro, Missouri
Hillsboro is a city in and the county seat of Jefferson County, Missouri, United States. The population was 3,473 at the 2020 census, up from 2,821 in 2010.
Jefferson County, Missouri in the context of Arnold, Missouri
Arnold is a city in northeastern Jefferson County, Missouri, situated near the confluence of the Meramec and Mississippi rivers. A suburb of St. Louis, the city lies within the Greater St. Louis metropolitan statistical area. The population was 20,858 at the 2020 United States census, which makes it the most populous community in the county.