King County area

Population and density of King County

The Census Bureau estimates that 2,344,939 people lived in King County on July 1, 2025. That ranks #13 of 3,222 county equivalents nationally and #1 of 39 in Washington. Since the April 1, 2020 estimates base of 2,269,668, the population has grown by 75,271 (+3.3%), compared with +3.8% for Washington as a whole.

With 2,115.8 square miles of land, that is 1,108 people per square mile (428 per km²), placing King County #168 nationally for density and #1 in Washington. The median county equivalent has 47 people per square mile; the Washington median is 39. Put another way, there are about 0.577 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 King County

39 incorporated places lie at least partly in King County. Together they are home to 2,102,432 people (89.7%); the other 242,507 (10.3%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Seattle city, with 784,777 residents in the county. Among places with at least 1,000 residents in 2020, Black Diamond city grew fastest since then (+48.6%).

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

Metropolitan area

King County is a central county of the Seattle-Tacoma-Bellevue, WA Metropolitan Statistical Area, in the Seattle-Bellevue-Kent, WA metropolitan division. Its 3 county equivalents have 4,161,883 residents on 5,870.3 square miles of land; King County accounts for 36% of the land and 56.3% of the residents. By combined land it ranks #37 of 393 metropolitan areas, and #15 by population. It belongs to the Seattle-Tacoma, WA Combined Statistical Area.

ZIP codes

89 ZIP Code Tabulation Areas have land in King County; 86 of them have most of their land inside the county, and the others mainly cover neighboring areas.

9800198002980039800498005980069800798008980109801198014980199802298023980249802598027980289802998030980319803298033980349803898039980409804298045980479805098051980529805398055980569805798058980599806598068980709807298074980759807798092981019810298103981049810598106981079810898109981129811598116981179811898119981219812298125981269813398134981369814498146981489815498155981589816498166981689817498177981789818898195981989819998224982889835498422

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 King County

King County shares a land border with 4 county equivalents. It has more land than 2 of them. The largest neighbor is Chelan County (2,921.2 mi²) and the smallest is Pierce County (1,668 mi²). Together with its neighbors, King County forms a block of 11,088.8 mi² of land, of which it holds 19.1%.

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

King County has more land than 2 of the 50 states. It is about 1.1 times the land area of Delaware (1,948.6 mi²), while Connecticut, the next larger state, has 2.3 times as much land (4,842.5 mi²). Washington’s county land could hold about 31 areas the size of King County.

Another way to picture it: the same land area would fill a square about 46 miles (74 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 King County?

King County has more land than 2,958 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 King County at #267 nationally by total area, 3 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 8.3%, compared with a national county-equivalent median of 1.2% — 7.1 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 King 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.