23 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Douglas township | 1 | 12,689 | 12,650 | 0.4% | 378 | 33.58 | Township |
| Effingham | 2 | 12,233 | 12,295 | -0.1% | 1,143 | 10.70 | City |
| Summit township | 3 | 3,700 | 3,786 | -0.22% | 110 | 33.64 | Township |
| Mound township | 4 | 3,508 | 3,558 | 0.03% | 95 | 36.97 | Township |
| Watson township | 5 | 3,148 | 3,207 | -0.13% | 88 | 35.83 | Township |
| Teutopolis township | 6 | 2,785 | 2,747 | 0.36% | 163 | 17.04 | Township |
| Altamont | 7 | 2,168 | 2,217 | -0.46% | 1,411 | 1.54 | City |
| Teutopolis | 8 | 1,687 | 1,626 | 0.72% | 826 | 2.04 | Village |
| Bishop township | 9 | 1,661 | 1,709 | -0.36% | 48 | 34.94 | Township |
| Mason township | 10 | 1,237 | 1,268 | -0.24% | 33 | 37.15 | Township |
| Jackson township | 11 | 1,212 | 1,239 | -0.25% | 32 | 37.46 | Township |
| St. Francis township | 12 | 1,168 | 1,178 | 0.17% | 36 | 32.38 | Township |
| Dieterich | 13 | 856 | 891 | -0.81% | 627 | 1.37 | Village |
| Watson | 14 | 651 | 670 | -0.61% | 596 | 1.09 | Village |
| Moccasin township | 15 | 485 | 498 | -0.21% | 14 | 35.59 | Township |
| Lucas township | 16 | 451 | 468 | -0.66% | 13 | 35.49 | Township |
| Banner township | 17 | 436 | 446 | -0.23% | 24 | 18.03 | Township |
| West township | 18 | 430 | 440 | -0.23% | 12 | 36.92 | Township |
| Beecher City | 19 | 415 | 429 | -0.72% | 464 | 0.90 | Village |
| Edgewood | 20 | 386 | 398 | -0.52% | 381 | 1.01 | Village |
| Mason | 21 | 315 | 325 | -0.63% | 245 | 1.29 | Town |
| Montrose | 22 | 207 | 211 | -0.48% | 325 | 0.64 | Village |
| Shumway | 23 | 179 | 184 | -0.56% | 539 | 0.33 | Village |
Douglas township is the largest city in Effingham County, with a population of 12,689.
Shumway is the smallest city in Effingham County.
There are 23 cities in Effingham County, Illinois.