23 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Douglas | 1 | 12,918 | 12,644 | 0.76% | 385 | 34 | Township |
| Effingham | 2 | 12,487 | 12,328 | 0.22% | 1,147 | 11 | City |
| Summit | 3 | 3,746 | 3,789 | 0.11% | 111 | 34 | Township |
| Mound | 4 | 3,536 | 3,560 | 0.17% | 96 | 37 | Township |
| Watson | 5 | 3,198 | 3,219 | 0.16% | 89 | 36 | Township |
| Teutopolis | 6 | 2,853 | 2,739 | 1.03% | 167 | 17 | Township |
| Altamont | 7 | 2,190 | 2,219 | -0.23% | 1,425 | 2 | City |
| Teutopolis | 8 | 1,727 | 1,627 | 0.99% | 845 | 2 | Village |
| Bishop | 9 | 1,685 | 1,712 | 0.12% | 48 | 35 | Township |
| Mason | 10 | 1,246 | 1,267 | 0% | 34 | 37 | Township |
| Jackson | 11 | 1,222 | 1,240 | -0.08% | 33 | 37 | Township |
| St. Francis | 12 | 1,173 | 1,178 | 0.17% | 36 | 32 | Township |
| Dieterich | 13 | 870 | 896 | -0.46% | 637 | 1 | Village |
| Watson | 14 | 651 | 668 | -0.46% | 596 | 1 | Village |
| Moccasin | 15 | 491 | 500 | 0% | 14 | 36 | Township |
| Lucas | 16 | 462 | 466 | 0.22% | 13 | 35 | Township |
| Banner | 17 | 442 | 445 | 0.45% | 25 | 18 | Township |
| West | 18 | 433 | 439 | 0% | 12 | 37 | Township |
| Beecher City | 19 | 420 | 429 | -0.24% | 469 | 1 | Village |
| Edgewood | 20 | 389 | 397 | -0.26% | 384 | 1 | Village |
| Mason | 21 | 319 | 325 | -0.31% | 248 | 1 | Town |
| Montrose | 22 | 215 | 217 | 0% | 338 | 1 | Village |
| Shumway | 23 | 185 | 188 | 0% | 557 | 0 | Village |
Douglas is the largest city in Effingham County, with a population of 12,918.
Shumway is the smallest city in Effingham County, with a population of 185.
There are 23 cities in Effingham County, Illinois.