Washington County area

Population and density of Washington County

The Census Bureau estimates that 611,708 people lived in Washington County on July 1, 2025. That ranks #114 of 3,222 county equivalents nationally and #2 of 36 in Oregon. Since the April 1, 2020 estimates base of 600,368, the population has grown by 11,340 (+1.9%), compared with +0.9% for Oregon as a whole.

With 724.3 square miles of land, that is 845 people per square mile (326 per km²), placing Washington County #219 nationally for density and #2 in Oregon. The median county equivalent has 47 people per square mile; the Oregon median is 25. Put another way, there are about 0.758 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

16 incorporated places lie at least partly in Washington County. Together they are home to 372,994 people (61%); the other 238,714 (39%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Hillsboro city, with 111,126 residents in the county. By land, Portland city is the largest at 133.5 mi² across all its counties. Among places with at least 1,000 residents in 2020, Wilsonville city grew fastest since then (+54.1%).

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 a central county of the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area. Its 7 county equivalents have 2,542,282 residents on 6,687.4 square miles of land; Washington County accounts for 10.8% of the land and 24.1% of the residents. By combined land it ranks #28 of 393 metropolitan areas, and #26 by population. It belongs to the Portland-Vancouver-Salem, OR-WA Combined Statistical Area.

ZIP codes

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

9700397005970069700797008970359705697062970649707097078971069710997113971169711797119971239712497125971329713397140971449721097219972219722397224972259722997231

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 5 county equivalents. It has more land than 3 of them. The largest neighbor is Clackamas County (1,870.7 mi²) and the smallest is Multnomah County (431 mi²). Together with its neighbors, Washington County forms a block of 5,503.8 mi² of land, of which it holds 13.2%.

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 1.4 times as much. Oregon’s county land could hold about 133 areas the size of Washington County.

Another way to picture it: the same land area would fill a square about 26.9 miles (43.3 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 Washington County?

Washington County has more land than 1,995 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 #1,331 nationally by total area, 104 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 0.3%, compared with a national county-equivalent median of 1.2% — 0.8 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.