County Maps US

St. Louis County, Missouri

The most populous of Missouri's 115 counties.

CountyFIPS 29189

Within Missouri
St. Louis County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Clayton, the county seat, located via the 2025 Census Gazetteer.

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Population
990,911
-12,454 (-1.2%) since 2020
Land area
508.5
square miles. A further 2.9% of the total area is water
Population density
1,949
people per square mile, computed rather than published
County seat
Clayton
Seat of county government.
Established
1812
213 years ago
Largest city
Florissant city
Population 51,124.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of St. Louis County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of St. Louis County, Missouri from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 770 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where St. Louis County ranks

Position among the 115 counties of Missouri, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn MissouriNationally
Population990,9111st of 11553rd of 3,144
Land area508.5 sq mi77th of 1152,041st of 3,144
Population density1,949 per sq mi2nd of 11575th of 3,144
Median household income$82,9367th of 115487th of 3,143

Full data for St. Louis County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population990,911Vintage 2025 Population Estimates
Population in 20201,003,365Vintage 2025 Population Estimates
2020 estimates base?1,004,548Vintage 2025 Population Estimates
Land area508.5 sq mi2025 Gazetteer Files
Water area15.4 sq mi2025 Gazetteer Files
Total area524 sq mi2025 Gazetteer Files
Population density?1,949 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$82,936American Community Survey 2020-2024 5-Year Estimates
Median home value$276,800American Community Survey 2020-2024 5-Year Estimates
Median age40.3American Community Survey 2020-2024 5-Year Estimates
Households413,849American Community Survey 2020-2024 5-Year Estimates
Housing units446,192American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
-1,316
9,583 births, 10,899 deaths
Net migration
+525
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 7 areas bordering St. Louis County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
St. Charles CountyMissouri48 mi426,499
Jefferson CountyMissouri41 mi233,132
St. Louis cityMissouri22 mi278,144
Franklin CountyMissouri12 mi108,090
Monroe CountyIllinois11 mi34,840
Madison CountyIllinois3.6 mi263,110
St. Clair CountyIllinois0.9 mi250,708

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

Side by side

All 115 counties of Missouri

Open the interactive Missouri county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.