13 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marietta | 1 | 12,913 | 13,355 | -0.68% | 1,532 | 8.43 | City |
| Belpre | 2 | 6,546 | 6,716 | -0.52% | 1,878 | 3.48 | City |
| Reno | 3 | 1,296 | 1,100 | 0.08% | 1,688 | 0.77 | CDP |
| Beverly | 4 | 1,195 | 1,230 | -0.58% | 1,752 | 0.68 | Village |
| Newport | 5 | 1,088 | 1,310 | 0.56% | 672 | 1.62 | CDP |
| Little Hocking | 6 | 720 | 759 | 4.35% | 1,735 | 0.41 | CDP |
| Lowell | 7 | 545 | 565 | -0.73% | 2,390 | 0.23 | Village |
| Waterford | 8 | 354 | 543 | -1.67% | 752 | 0.47 | CDP |
| Vincent | 9 | 142 | 273 | -8.39% | 371 | 0.38 | CDP |
| Macksburg | 10 | 112 | 116 | -0.89% | 519 | 0.22 | Village |
| Newport | 11 | 84 | 100 | -8.7% | 234 | 0.36 | CDP |
| Lower Salem | 12 | 72 | 76 | -1.37% | 1,220 | 0.06 | Village |
| Graysville | 13 | 67 | 69 | 0% | 67 | 1.01 | Village |
Marietta is the largest city in Washington County, with a population of 12,913.
Graysville is the smallest city in Washington County.
There are 13 cities in Washington County, Ohio.