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County · code 29189

St. Louis CountyMissouri

St. Louis County is a county in Missouri with its seat in Clayton. The county was founded in 1812 and is named after Louis IX of France.

  • Founded1812
  • County seatClayton
  • Named forLouis IX of France
  • Land area508 sq mi + 15 sq mi water
  • Population1,004,125 2020 Census
  • Parcels mapped401,522 checked 15 October 2026
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Updated

St. Louis citySt. CharlesJeffersonMonroe, ILSt. Clair, ILMadison, ILFranklin Clayton Census outline · seat marked

Where it is

St. Louis on the map of Missouri

Missouri has 115 counties and county equivalents, each with its own records office. Shapes with a page are links.

Adair CountyAndrew CountyAtchison CountyAudrain CountyBarry CountyBarton CountyBates CountyBenton CountyBollinger CountyBoone CountyBuchanan CountyButler CountyCaldwell CountyCallaway CountyCamden CountyCape Girardeau CountyCarroll CountyCarter CountyCass CountyCedar CountyChariton CountyChristian CountyClark CountyClay CountyClinton CountyCole CountyCooper CountyCrawford CountyDade CountyDallas CountyDaviess CountyDeKalb CountyDent CountyDouglas CountyDunklin CountyFranklin CountyGasconade CountyGentry CountyGreene CountyGrundy CountyHarrison CountyHenry CountyHickory CountyHolt CountyHoward CountyHowell CountyIron CountyJackson CountyJasper CountyJefferson CountyJohnson CountyKnox CountyLaclede CountyLafayette CountyLawrence CountyLewis CountyLincoln CountyLinn CountyLivingston CountyMcDonald CountyMacon CountyMadison CountyMaries CountyMarion CountyMercer CountyMiller CountyMississippi CountyMoniteau CountyMonroe CountyMontgomery CountyMorgan CountyNew Madrid CountyNewton CountyNodaway CountyOregon CountyOsage CountyOzark CountyPemiscot CountyPerry CountyPettis CountyPhelps CountyPike CountyPlatte CountyPolk CountyPulaski CountyPutnam CountyRalls CountyRandolph CountyRay CountyReynolds CountyRipley CountySt. Charles CountySt. Clair CountySte. Genevieve CountySt. Francois CountySaline CountySchuyler CountyScotland CountyScott CountyShannon CountyShelby CountyStoddard CountyStone CountySullivan CountyTaney CountyTexas CountyVernon CountyWarren CountyWashington CountyWayne CountyWebster CountyWorth CountyWright CountySt. Louis citySt. Louis County St. Louis
Counties of Missouri · St. Louis highlighted

History

Founded in 1812

An old deed may name a county that no longer exists, or a boundary that has since moved.

St. Louis District was created on October 1, 1804, within the District of Louisiana from the Louisiana Purchase. On July 4, 1805, the District of Louisiana was renamed Louisiana Territory, and St. Louis District became a district in the new territory. On December 7, 1812, Louisiana Territory was renamed Missouri Territory, and most of St. Louis reverted to non-county area.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

  1. 1804
    St. Louis County created St. Louis District (now St. Louis) created within the District of Louisiana. · Terr. Papers U.S., 13: 51-52; U.S. Stat., vol. 2, ch. 38 [1804]/pp. 283-289; Violette, 46-47
  2. 1805
    Renamed St. Louis (Missouri) became a district (county) in Louisiana Territory when the District of Louisiana was renamed Louisiana Territory.
    formerly St. Louis Became A District In Louisiana Territory When the District of Louisiana Was
    · U.S. Stat., vol. 2, ch. 31[1805]/pp. 331-332
  3. 1812
    Gained territory St. Louis District became St. Louis County; St. Louis gained from Ste. Genevieve and lost to creation of Non-County Area 1 when its western boundary was redefined as the boundary of the "Osage Purchase."
    from Ste. Genevieve
    · Terr. Papers U.S., 14:599-601; U.S. Stat., vol. 2, ch. 95[1812]/pp. 743-747; Royce, 676-677, pls. 112, 144
  4. 1813
    Lost territory St. Louis lost to creation of Washington.
    to Washington
    · Mo. Terr. Laws 1813-1814, ch. 95, secs. 1,11/pp. 285-290; Violette, 78
  5. 1813
    Exchanged territory St. Louis exchanged with Washington, lost to Ste. Genevieve.
    with Washingtonwith Ste. Genevieve
    · Mo. Terr. Laws 1813-1814, ch. 99, sec. 1/pp. 293-295
Show all 8 changes (3 more)
  1. 1804
    St. Louis County created St. Louis District (now St. Louis) created within the District of Louisiana. · Terr. Papers U.S., 13: 51-52; U.S. Stat., vol. 2, ch. 38 [1804]/pp. 283-289; Violette, 46-47
  2. 1805
    Renamed St. Louis (Missouri) became a district (county) in Louisiana Territory when the District of Louisiana was renamed Louisiana Territory.
    formerly St. Louis Became A District In Louisiana Territory When the District of Louisiana Was
    · U.S. Stat., vol. 2, ch. 31[1805]/pp. 331-332
  3. 1812
    Gained territory St. Louis District became St. Louis County; St. Louis gained from Ste. Genevieve and lost to creation of Non-County Area 1 when its western boundary was redefined as the boundary of the "Osage Purchase."
    from Ste. Genevieve
    · Terr. Papers U.S., 14:599-601; U.S. Stat., vol. 2, ch. 95[1812]/pp. 743-747; Royce, 676-677, pls. 112, 144
  4. 1813
    Lost territory St. Louis lost to creation of Washington.
    to Washington
    · Mo. Terr. Laws 1813-1814, ch. 95, secs. 1,11/pp. 285-290; Violette, 78
  5. 1813
    Exchanged territory St. Louis exchanged with Washington, lost to Ste. Genevieve.
    with Washingtonwith Ste. Genevieve
    · Mo. Terr. Laws 1813-1814, ch. 99, sec. 1/pp. 293-295
  6. 1816
    Lost territory St. Louis lost to creation of Howard.
    to Howard
    · Mo. Terr. Laws 1815-1816, ch. 162, secs. 1, 8/pp. 460-464
  7. 1819
    Lost territory St. Louis lost to creation of Franklin and Jefferson.
    to Franklinto Jefferson
    · Mo. Terr. Laws 1818-1819, chs. 220, 225/pp. 554-558, 562-566
  8. 1876
    Lost territory St. Louis lost to creation of St. Louis City.
    to St. Louis City
    · Hyde and Conard, 4: 1993-1996

Land and parcels

What the maps cover in St. Louis

Who publishes each layer, how good it is, and when we last checked.

Official
from the office that keeps the record
Good enough
a reliable statewide or national copy
Fallback
a guide only; check the official record
Missing
nothing public found yet

People and land

St. Louis by the Census

Population
1,004,125 2020 Census count
Housing units
444,653 2020 Census count
Land area
508 square miles
Water area
15 square miles
People per sq mi
1,977 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

See your own lot on these maps

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Questions

Common questions about St. Louis County

When was St. Louis County founded?
St. Louis County was founded in 1812, and named after Louis IX of France.
What is the county seat of St. Louis County?
The county seat of St. Louis County is Clayton.
Is there an online parcel map for St. Louis County?
Yes. St. Louis County publishes a parcel map of 401,522 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has St. Louis County's boundary or name changed?
St. Louis County was created in 1804. Since then the Atlas of Historical County Boundaries records 7 later changes, chiefly involving Ste. Genevieve County, Washington County and Franklin County. It was formerly called St. Louis Became A District In Louisiana Territory When the District of Louisiana Was.
Is my lot in a flood zone?
We do not have flood maps for St. Louis County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby

Counties next door