24 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marietta | 1 | 12,958 | 13,361 | -0.62% | 1,537 | 8 | City |
| Belpre | 2 | 6,555 | 6,719 | -0.5% | 1,881 | 3 | City |
| Muskingum | 3 | 4,260 | 4,372 | -0.3% | 201 | 21 | Township |
| Marietta | 4 | 4,174 | 4,277 | -0.26% | 282 | 15 | Township |
| Belpre | 5 | 3,804 | 3,909 | -0.34% | 163 | 23 | Township |
| Waterford | 6 | 3,467 | 3,553 | -0.2% | 93 | 37 | Township |
| Barlow | 7 | 2,513 | 2,583 | -0.32% | 79 | 32 | Township |
| Dunham | 8 | 2,500 | 2,555 | -0.2% | 107 | 23 | Township |
| Newport | 9 | 1,874 | 1,927 | -0.37% | 53 | 35 | Township |
| Adams | 10 | 1,489 | 1,537 | -0.53% | 48 | 31 | Township |
| Watertown | 11 | 1,471 | 1,511 | -0.27% | 41 | 36 | Township |
| Grandview | 12 | 1,369 | 1,407 | -0.36% | 39 | 35 | Township |
| Beverly | 13 | 1,203 | 1,231 | -0.5% | 1,764 | 1 | Village |
| Wesley | 14 | 938 | 960 | -0.21% | 30 | 31 | Township |
| Fearing | 15 | 857 | 873 | -0.12% | 37 | 23 | Township |
| Lawrence | 16 | 793 | 811 | -0.25% | 23 | 35 | Township |
| Palmer | 17 | 556 | 564 | -0.18% | 25 | 23 | Township |
| Lowell | 18 | 544 | 564 | -0.73% | 2,386 | 0 | Village |
| Liberty | 19 | 424 | 434 | -0.24% | 14 | 29 | Township |
| Aurelius | 20 | 301 | 305 | 0.33% | 22 | 14 | Township |
| Ludlow | 21 | 258 | 267 | -0.39% | 12 | 22 | Township |
| Macksburg | 22 | 112 | 116 | -0.88% | 519 | 0 | Village |
| Lower Salem | 23 | 69 | 74 | -1.43% | 1,169 | 0 | Village |
| Graysville | 24 | 65 | 68 | -1.52% | 65 | 1 | Village |
Marietta is the largest city in Washington County, with a population of 12,958.
Graysville is the smallest city in Washington County, with a population of 65.
There are 24 cities in Washington County, Ohio.