22 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hillsboro | 1 | 111,150 | 107,084 | 0.74% | 4,301 | 26 | City |
| Beaverton | 2 | 98,488 | 97,558 | 0.19% | 5,014 | 20 | City |
| Tigard | 3 | 57,867 | 55,034 | 0.99% | 4,537 | 13 | City |
| Aloha | 4 | 54,559 | 53,724 | 0.63% | 7,417 | 7 | CDP |
| Tualatin | 5 | 28,074 | 27,884 | 0.14% | 3,343 | 8 | City |
| Forest Grove | 6 | 27,323 | 26,088 | 0.91% | 4,638 | 6 | City |
| Sherwood | 7 | 20,438 | 20,452 | -0.01% | 4,176 | 5 | City |
| Cornelius | 8 | 16,008 | 12,813 | 4.16% | 6,844 | 2 | City |
| Oak Hills | 9 | 11,892 | 11,682 | 0.32% | 7,648 | 2 | CDP |
| Cedar Hills | 10 | 9,270 | 9,514 | 0.71% | 4,918 | 2 | CDP |
| Garden Home-Whitford | 11 | 7,189 | 7,295 | 0.48% | 4,641 | 2 | CDP |
| Raleigh Hills | 12 | 6,947 | 6,675 | 1.02% | 4,567 | 2 | CDP |
| West Slope | 13 | 6,690 | 6,799 | 0.13% | 4,140 | 2 | CDP |
| Marlene Village | 14 | 6,608 | 5,356 | 7.15% | 7,230 | 1 | CDP |
| King City | 15 | 4,958 | 5,176 | -0.88% | 6,113 | 1 | City |
| Metzger | 16 | 3,974 | 4,402 | 0.35% | 5,229 | 1 | CDP |
| North Plains | 17 | 3,419 | 3,443 | -0.15% | 3,137 | 1 | City |
| Durham | 18 | 1,864 | 1,944 | -0.85% | 4,546 | 0 | City |
| Banks | 19 | 1,829 | 1,838 | -0.11% | 2,400 | 1 | City |
| Gaston | 20 | 675 | 680 | -0.15% | 1,979 | 0 | City |
| Cherry Grove | 21 | 611 | 506 | 7.19% | 565 | 1 | CDP |
| Dilley | 22 | 305 | 172 | 7.02% | 408 | 1 | CDP |
Hillsboro is the largest city in Washington County, with a population of 111,150.
Dilley is the smallest city in Washington County, with a population of 305.
There are 22 cities in Washington County, Oregon.