22 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Havana | 1 | 4,085 | 4,386 | -1.42% | 71 | 57.86 | Township |
| Havana | 2 | 2,741 | 2,956 | -1.54% | 987 | 2.78 | City |
| Mason City | 3 | 2,167 | 2,329 | -1.46% | 61 | 35.46 | Township |
| Manito | 4 | 2,083 | 2,238 | -1.47% | 48 | 43.77 | Township |
| Mason City | 5 | 1,922 | 2,069 | -1.49% | 1,897 | 1.01 | City |
| Manito | 6 | 1,434 | 1,551 | -1.58% | 948 | 1.51 | Village |
| Bath | 7 | 690 | 738 | -1.43% | 10 | 66.78 | Township |
| Quiver | 8 | 669 | 715 | -1.33% | 16 | 42.49 | Township |
| San Jose | 9 | 449 | 478 | -1.32% | 1,085 | 0.41 | Village |
| Kilbourne | 10 | 443 | 474 | -1.34% | 11 | 40.09 | Township |
| Forest City | 11 | 434 | 464 | -1.59% | 13 | 33.31 | Township |
| Allens Grove | 12 | 433 | 465 | -1.37% | 12 | 35.73 | Township |
| Easton | 13 | 292 | 316 | -1.68% | 1,217 | 0.24 | Village |
| Bath | 14 | 256 | 275 | -1.54% | 701 | 0.36 | Village |
| Kilbourne | 15 | 250 | 267 | -1.19% | 281 | 0.89 | Village |
| Lynchburg | 16 | 222 | 236 | -1.33% | 5 | 42.16 | Township |
| Salt Creek | 17 | 206 | 220 | -1.44% | 6 | 35.82 | Township |
| Forest City | 18 | 203 | 217 | -1.46% | 388 | 0.52 | Village |
| Goofy Ridge | 19 | 172 | 238 | -6.52% | 128 | 1.35 | CDP |
| Pennsylvania | 20 | 145 | 156 | -1.36% | 4 | 35.85 | Township |
| Crane Creek | 21 | 139 | 149 | -1.42% | 4 | 34.01 | Township |
| Topeka | 22 | 53 | 58 | -1.85% | 387 | 0.14 | Village |
Havana is the largest city in Mason County, with a population of 4,085.
Topeka is the smallest city in Mason County, with a population of 53.
There are 22 cities in Mason County, Illinois.