27 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Nashville | 1 | 3,329 | 3,474 | -0.95% | 96 | 35 | Township |
| Nashville | 2 | 2,961 | 3,090 | -0.87% | 961 | 3 | City |
| Okawville | 3 | 1,919 | 1,951 | -0.36% | 53 | 36 | Township |
| Okawville | 4 | 1,341 | 1,366 | -0.37% | 662 | 2 | Village |
| Irvington | 5 | 1,134 | 1,169 | -0.7% | 23 | 48 | Township |
| Hoyleton | 6 | 1,009 | 1,042 | -0.69% | 20 | 51 | Township |
| Ashley | 7 | 730 | 756 | -0.95% | 30 | 24 | Township |
| Du Bois | 8 | 641 | 646 | -0.47% | 17 | 37 | Township |
| Lively Grove | 9 | 563 | 570 | -0.35% | 16 | 36 | Township |
| Irvington | 10 | 562 | 582 | -0.71% | 556 | 1 | Village |
| Beaucoup | 11 | 558 | 570 | -0.53% | 15 | 38 | Township |
| Oakdale | 12 | 537 | 546 | -0.56% | 14 | 37 | Township |
| Pilot Knob | 13 | 500 | 515 | -0.99% | 14 | 35 | Township |
| Hoyleton | 14 | 496 | 518 | -0.8% | 653 | 1 | Village |
| Johannisburg | 15 | 493 | 508 | -0.8% | 14 | 36 | Township |
| Plum Hill | 16 | 485 | 491 | -0.21% | 13 | 38 | Township |
| Ashley | 17 | 444 | 461 | -0.67% | 394 | 1 | City |
| Bolo | 18 | 400 | 396 | 0.25% | 11 | 37 | Township |
| Venedy | 19 | 387 | 394 | -0.51% | 17 | 22 | Township |
| Covington | 20 | 374 | 379 | -0.27% | 9 | 40 | Township |
| Richview | 21 | 303 | 316 | -0.98% | 25 | 12 | Township |
| Addieville | 22 | 249 | 253 | -0.4% | 251 | 1 | Village |
| Richview | 23 | 227 | 236 | -0.87% | 198 | 1 | Village |
| Oakdale | 24 | 193 | 197 | -0.52% | 122 | 2 | Village |
| Du Bois | 25 | 181 | 178 | 0.56% | 172 | 1 | Village |
| Radom | 26 | 180 | 182 | 0% | 172 | 1 | Village |
| Venedy | 27 | 124 | 126 | 0% | 441 | 0 | Village |
Nashville is the largest city in Washington County, with a population of 3,329.
Venedy is the smallest city in Washington County, with a population of 124.
There are 27 cities in Washington County, Illinois.