St. Louis County area

Population and density of St. Louis County

The Census Bureau estimates that 990,911 people lived in St. Louis County on July 1, 2025. That ranks #53 of 3,222 county equivalents nationally and #1 of 115 in Missouri. Since the April 1, 2020 estimates base of 1,004,548, the population has declined by 13,637 (−1.4%), compared with +1.9% for Missouri as a whole.

With 508.5 square miles of land, that is 1,949 people per square mile (752 per km²), placing St. Louis County #84 nationally for density and #2 in Missouri. The median county equivalent has 47 people per square mile; the Missouri median is 31. Put another way, there are about 0.328 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in St. Louis County

87 incorporated places lie at least partly in St. Louis County. Together they are home to 674,627 people (68.1%); the other 316,284 (31.9%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Florissant city, with 51,124 residents in the county. The county seat, Clayton city, has 17,807 residents. By land, Wildwood city is the largest at 67 mi². Among places with at least 1,000 residents in 2020, Eureka city grew fastest since then (+14.7%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside St. Louis County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

St. Louis County is a central county of the St. Louis, MO-IL Metropolitan Statistical Area. Its 15 county equivalents have 2,814,421 residents on 7,863.5 square miles of land; St. Louis County accounts for 6.5% of the land and 35.2% of the residents. By combined land it ranks #19 of 393 metropolitan areas, and #23 by population. It belongs to the St. Louis-St. Charles-Farmington, MO-IL Combined Statistical Area.

ZIP codes

47 ZIP Code Tabulation Areas have land in St. Louis County; 43 of them have most of their land inside the county, and the others mainly cover neighboring areas.

6300563011630176302163025630266303163033630346303863040630426304363044630456304963069630746308863105631146311763119631206312163122631236312463125631266312763128631296313063131631326313363134631356313663137631386314063141631436314463146

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering St. Louis County

St. Louis County shares a land border with 7 county equivalents, including 3 in Illinois. It has more land than 2 of them. The largest neighbor is Franklin County (922.5 mi²) and the smallest is St. Louis city (61.7 mi²). Together with its neighbors, St. Louis County forms a block of 4,467.7 mi² of land, of which it holds 11.4%.

How big is St. Louis County compared with U.S. states?

St. Louis County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2 times as much. Missouri’s county land could hold about 135 areas the size of St. Louis County.

Another way to picture it: the same land area would fill a square about 22.6 miles (36.3 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about St. Louis County?

St. Louis County has more land than 1,181 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places St. Louis County at #2,092 nationally by total area, 51 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 2.9%, compared with a national county-equivalent median of 1.2% — 1.8 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside St. Louis County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.