Franklin County area

Population and density of Franklin County

The Census Bureau estimates that 108,090 people lived in Franklin County on July 1, 2025. That ranks #588 of 3,222 county equivalents nationally and #12 of 115 in Missouri. Since the April 1, 2020 estimates base of 104,680, the population has grown by 3,410 (+3.3%), compared with +1.9% for Missouri as a whole.

With 922.5 square miles of land, that is 117 people per square mile (45 per km²), placing Franklin County #889 nationally for density and #17 in Missouri. The median county equivalent has 47 people per square mile; the Missouri median is 31. Put another way, there are about 5.5 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 Franklin County

13 incorporated places lie at least partly in Franklin County. Together they are home to 51,709 people (47.8%); the other 56,381 (52.2%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Washington city, with 15,906 residents in the county. The county seat, Union city, has 13,445 residents. Among places with at least 1,000 residents in 2020, Union city grew fastest since then (+8.9%).

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

Metropolitan area

Franklin County is an outlying 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; Franklin County accounts for 11.7% of the land and 3.8% 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

23 ZIP Code Tabulation Areas have land in Franklin County; 19 of them have most of their land inside the county, and the others mainly cover neighboring areas.

6300563013630146301563037630396304163055630566306063061630686306963072630736307763079630806308463089630906309165441

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 Franklin County

Franklin County shares a land border with 7 county equivalents. It has more land than every one of them. The largest neighbor is Washington County (759.9 mi²) and the smallest is Warren County (428.6 mi²). Together with its neighbors, Franklin County forms a block of 5,097.3 mi² of land, of which it holds 18.1%.

How big is Franklin County compared with U.S. states?

Franklin County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.1 times as much. Missouri’s county land could hold about 75 areas the size of Franklin County.

Another way to picture it: the same land area would fill a square about 30.4 miles (48.9 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 Franklin County?

Franklin County has more land than 2,430 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 Franklin County at #882 nationally by total area, 90 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 0.9%, compared with a national county-equivalent median of 1.2% — 0.3 percentage points lower. 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 Franklin 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.