27 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Nashville | 1 | 3,367 | 3,480 | -0.56% | 97 | 35 | Township |
| Nashville | 2 | 2,983 | 3,097 | -0.77% | 968 | 3 | City |
| Okawville | 3 | 1,923 | 1,953 | -0.41% | 53 | 36 | Township |
| Okawville | 4 | 1,342 | 1,366 | -0.37% | 663 | 2 | Village |
| Irvington | 5 | 1,146 | 1,171 | -0.26% | 24 | 48 | Township |
| Hoyleton | 6 | 1,023 | 1,044 | -0.2% | 20 | 51 | Township |
| Ashley | 7 | 739 | 755 | -0.4% | 30 | 24 | Township |
| Du Bois | 8 | 641 | 646 | -0.31% | 17 | 37 | Township |
| Beaucoup | 9 | 568 | 569 | 0.35% | 15 | 38 | Township |
| Lively Grove | 10 | 568 | 570 | -0.18% | 16 | 36 | Township |
| Irvington | 11 | 562 | 582 | -0.71% | 556 | 1 | Village |
| Oakdale | 12 | 549 | 547 | 0.18% | 15 | 37 | Township |
| Pilot Knob | 13 | 513 | 514 | 0% | 15 | 35 | Township |
| Johannisburg | 14 | 506 | 508 | 0.4% | 14 | 36 | Township |
| Hoyleton | 15 | 501 | 519 | -0.79% | 659 | 1 | Village |
| Plum Hill | 16 | 488 | 493 | -0.2% | 13 | 38 | Township |
| Ashley | 17 | 444 | 459 | -0.67% | 394 | 1 | City |
| Bolo | 18 | 396 | 395 | 0% | 11 | 37 | Township |
| Venedy | 19 | 389 | 391 | 0% | 17 | 22 | Township |
| Covington | 20 | 374 | 379 | 0% | 9 | 40 | Township |
| Richview | 21 | 310 | 316 | -0.32% | 26 | 12 | Township |
| Addieville | 22 | 252 | 257 | -0.4% | 254 | 1 | Village |
| Richview | 23 | 229 | 236 | -0.87% | 199 | 1 | Village |
| Oakdale | 24 | 197 | 197 | 0% | 125 | 2 | Village |
| Radom | 25 | 180 | 183 | -0.55% | 172 | 1 | Village |
| Du Bois | 26 | 179 | 178 | 0% | 170 | 1 | Village |
| Venedy | 27 | 122 | 125 | -0.81% | 434 | 0 | Village |
Nashville is the largest city in Washington County, with a population of 3,367.
Venedy is the smallest city in Washington County, with a population of 122.
There are 27 cities in Washington County, Illinois.