Washington County area

Population and density of Washington County

The Census Bureau estimates that 13,564 people lived in Washington County on July 1, 2025. That ranks #2,257 of 3,222 county equivalents nationally and #75 of 102 in Illinois. Since the April 1, 2020 estimates base of 13,765, the population has declined by 201 (−1.5%), compared with −0.8% for Illinois as a whole.

With 562.6 square miles of land, that is 24 people per square mile (9.3 per km²), placing Washington County #2,171 nationally for density and #84 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 27 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 Washington County

14 incorporated places lie at least partly in Washington County. Together they are home to 7,333 people (54.1%); the other 6,231 (45.9%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Nashville city, with 3,011 residents in the county. By land, Centralia city is the largest at 8.2 mi² across all its counties.

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

Metropolitan area

Washington County is not part of any metropolitan or micropolitan statistical area in the Office of Management and Budget’s July 2023 delineation; 1,306 other county equivalents are also outside one. These areas are built around an urban core of at least 10,000 people plus the counties tied to it by commuting, so counties outside them are generally rural.

ZIP codes

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

62214622376225762263622686227162801628036280862831628486287662877

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 Washington County

Washington County shares a land border with 6 county equivalents. It has more land than 2 of them. The largest neighbor is St. Clair County (657.7 mi²) and the smallest is Perry County (441.9 mi²). Together with its neighbors, Washington County forms a block of 3,855.4 mi² of land, of which it holds 14.6%.

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

Washington County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.8 times as much. Illinois’s county land could hold about 99 areas the size of Washington County.

Another way to picture it: the same land area would fill a square about 23.7 miles (38.2 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 Washington County?

Washington County has more land than 1,385 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 Washington County at #1,958 nationally by total area, 121 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 0.2%, compared with a national county-equivalent median of 1.2% — 0.9 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 Washington 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.