Clinton County area

Population and density of Clinton County

The Census Bureau estimates that 37,128 people lived in Clinton County on July 1, 2025. That ranks #1,292 of 3,222 county equivalents nationally and #35 of 102 in Illinois. Since the April 1, 2020 estimates base of 36,904, the population has grown by 224 (+0.6%), compared with −0.8% for Illinois as a whole.

With 473.9 square miles of land, that is 78 people per square mile (30 per km²), placing Clinton County #1,177 nationally for density and #30 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 8.2 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 Clinton County

16 incorporated places lie at least partly in Clinton County. Together they are home to 24,643 people (66.4%); the other 12,485 (33.6%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Breese city, with 4,602 residents in the county. The county seat, Carlyle city, has 3,188 residents. By land, Centralia city is the largest at 8.2 mi² across all its counties. Among places with at least 1,000 residents in 2020, Aviston village grew fastest since then (+4.7%).

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

Metropolitan area

Clinton 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; Clinton County accounts for 6% of the land and 1.3% 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

17 ZIP Code Tabulation Areas have land in Clinton County; 10 of them have most of their land inside the county, and the others mainly cover neighboring areas.

6221562216622186221962230622316224562249622506225362265622666227562293628016287562882

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 Clinton County

Clinton County shares a land border with 6 county equivalents. It has more land than 1 of them. The largest neighbor is Fayette County (716.5 mi²) and the smallest is Bond County (380.3 mi²). Together with its neighbors, Clinton County forms a block of 4,079.1 mi² of land, of which it holds 11.6%.

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

Clinton County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.2 times as much. Illinois’s county land could hold about 117 areas the size of Clinton County.

Another way to picture it: the same land area would fill a square about 21.8 miles (35 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 Clinton County?

Clinton County has more land than 1,047 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 Clinton County at #2,169 nationally by total area, 6 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.

Its water share is 5.8%, compared with a national county-equivalent median of 1.2% — 4.6 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 Clinton 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.