22 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Havana | 1 | 4,189 | 4,384 | -0.4% | 72 | 58 | Township |
| Havana | 2 | 2,794 | 2,953 | -1.13% | 1,006 | 3 | City |
| Mason City | 3 | 2,221 | 2,326 | -0.45% | 63 | 35 | Township |
| Manito | 4 | 2,146 | 2,239 | -0.28% | 49 | 44 | Township |
| Mason City | 5 | 1,960 | 2,068 | -1.11% | 1,935 | 1 | City |
| Manito | 6 | 1,472 | 1,552 | -1.08% | 973 | 2 | Village |
| Bath | 7 | 708 | 737 | -0.28% | 11 | 67 | Township |
| Quiver | 8 | 689 | 716 | -0.29% | 16 | 42 | Township |
| San Jose | 9 | 465 | 485 | -0.85% | 1,123 | 0 | Village |
| Kilbourne | 10 | 451 | 471 | -0.66% | 11 | 40 | Township |
| Forest City | 11 | 450 | 466 | -0.22% | 14 | 33 | Township |
| Allens Grove | 12 | 446 | 464 | 0% | 12 | 36 | Township |
| Easton | 13 | 298 | 315 | -1.32% | 1,242 | 0 | Village |
| Bath | 14 | 262 | 275 | -1.13% | 718 | 0 | Village |
| Kilbourne | 15 | 256 | 268 | -1.16% | 288 | 1 | Village |
| Lynchburg | 16 | 222 | 231 | -0.45% | 5 | 42 | Township |
| Salt Creek | 17 | 211 | 220 | -0.47% | 6 | 36 | Township |
| Forest City | 18 | 208 | 218 | -0.95% | 398 | 1 | Village |
| Goofy Ridge | 19 | 172 | 238 | -6.52% | 128 | 1 | CDP |
| Pennsylvania | 20 | 150 | 156 | 0% | 4 | 36 | Township |
| Crane Creek | 21 | 149 | 155 | 0% | 4 | 34 | Township |
| Topeka | 22 | 55 | 58 | -1.79% | 401 | 0 | Village |
Havana is the largest city in Mason County, with a population of 4,189.
Topeka is the smallest city in Mason County, with a population of 55.
There are 22 cities in Mason County, Illinois.