30 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 |
| Muskingum township | 3 | 4,240 | 4,370 | -0.56% | 200 | 21.20 | Township |
| Marietta township | 4 | 4,164 | 4,275 | -0.48% | 281 | 14.82 | Township |
| Belpre township | 5 | 3,790 | 3,905 | -0.58% | 162 | 23.33 | Township |
| Waterford township | 6 | 3,451 | 3,551 | -0.52% | 93 | 37.23 | Township |
| Dunham township | 7 | 2,508 | 2,557 | -0.36% | 108 | 23.29 | Township |
| Barlow township | 8 | 2,499 | 2,583 | -0.64% | 79 | 31.64 | Township |
| Newport township | 9 | 1,870 | 1,928 | -0.53% | 53 | 35.22 | Township |
| Adams township | 10 | 1,489 | 1,536 | -0.53% | 48 | 30.93 | Township |
| Watertown township | 11 | 1,468 | 1,515 | -0.54% | 40 | 36.27 | Township |
| Grandview township | 12 | 1,366 | 1,407 | -0.51% | 39 | 35.11 | Township |
| Reno | 13 | 1,296 | 1,100 | 0.08% | 1,688 | 0.77 | CDP |
| Beverly | 14 | 1,195 | 1,230 | -0.58% | 1,752 | 0.68 | Village |
| Newport | 15 | 1,088 | 1,310 | 0.55% | 672 | 1.62 | CDP |
| Wesley township | 16 | 942 | 958 | -0.32% | 30 | 31.07 | Township |
| Fearing township | 17 | 850 | 875 | -0.58% | 36 | 23.44 | Township |
| Lawrence township | 18 | 781 | 811 | -0.76% | 22 | 35.04 | Township |
| Little Hocking | 19 | 720 | 759 | 4.35% | 1,735 | 0.41 | CDP |
| Palmer township | 20 | 548 | 564 | -0.54% | 24 | 22.54 | Township |
| Lowell | 21 | 545 | 565 | -0.73% | 2,390 | 0.23 | Village |
| Liberty township | 22 | 421 | 434 | -0.47% | 14 | 29.49 | Township |
| Waterford | 23 | 354 | 543 | -1.67% | 752 | 0.47 | CDP |
| Aurelius township | 24 | 295 | 305 | -0.34% | 21 | 13.99 | Township |
| Ludlow township | 25 | 255 | 268 | -1.16% | 11 | 22.28 | Township |
| Vincent | 26 | 142 | 273 | -8.39% | 371 | 0.38 | CDP |
| Macksburg | 27 | 112 | 116 | -0.88% | 519 | 0.22 | Village |
| Newport | 28 | 84 | 100 | -8.7% | 234 | 0.36 | CDP |
| Lower Salem | 29 | 72 | 76 | -1.37% | 1,220 | 0.06 | Village |
| Graysville | 30 | 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 30 cities in Washington County, Ohio.