22 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hillsboro | 1 | 108,223 | 106,990 | 0.23% | 4,188 | 25.84 | City |
| Beaverton | 2 | 96,568 | 97,510 | -0.19% | 4,917 | 19.64 | City |
| Tigard | 3 | 55,972 | 55,017 | 0.34% | 4,388 | 12.76 | City |
| Aloha | 4 | 54,559 | 53,724 | 0.63% | 7,417 | 7.36 | CDP |
| Forest Grove | 5 | 27,177 | 26,231 | 0.7% | 4,613 | 5.89 | City |
| Tualatin | 6 | 27,049 | 27,884 | -0.61% | 3,221 | 8.40 | City |
| Sherwood | 7 | 19,645 | 20,424 | -0.79% | 4,014 | 4.89 | City |
| Cornelius | 8 | 16,440 | 12,792 | 4.65% | 7,029 | 2.34 | City |
| Oak Hills | 9 | 11,892 | 11,682 | 0.32% | 7,648 | 1.55 | CDP |
| Cedar Hills | 10 | 9,270 | 9,514 | 0.71% | 4,918 | 1.89 | CDP |
| Garden Home-Whitford | 11 | 7,189 | 7,295 | 0.48% | 4,641 | 1.55 | CDP |
| Raleigh Hills | 12 | 6,947 | 6,675 | 1.02% | 4,567 | 1.52 | CDP |
| West Slope | 13 | 6,690 | 6,799 | 0.13% | 4,140 | 1.62 | CDP |
| Marlene Village | 14 | 6,608 | 5,356 | 7.15% | 7,230 | 0.91 | CDP |
| King City | 15 | 4,829 | 5,176 | -1.41% | 5,954 | 0.81 | City |
| Metzger | 16 | 3,974 | 4,402 | 0.35% | 5,229 | 0.76 | CDP |
| North Plains | 17 | 3,334 | 3,443 | -0.66% | 3,059 | 1.09 | City |
| Durham | 18 | 1,806 | 1,941 | -1.47% | 4,405 | 0.41 | City |
| Banks | 19 | 1,785 | 1,839 | -0.61% | 2,343 | 0.76 | City |
| Gaston | 20 | 660 | 677 | -0.45% | 1,935 | 0.34 | City |
| Cherry Grove | 21 | 611 | 506 | 7.19% | 565 | 1.08 | CDP |
| Dilley | 22 | 305 | 172 | 7.02% | 408 | 0.75 | CDP |
Hillsboro is the largest city in Washington County, with a population of 108,223.
Dilley is the smallest city in Washington County.
There are 22 cities in Washington County, Oregon.