10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Havana | 1 | 2,741 | 2,956 | -1.54% | 987 | 2.78 | City |
| Mason City | 2 | 1,922 | 2,069 | -1.49% | 1,897 | 1.01 | City |
| Manito | 3 | 1,434 | 1,551 | -1.58% | 948 | 1.51 | Village |
| San Jose | 4 | 449 | 478 | -1.32% | 1,085 | 0.41 | Village |
| Easton | 5 | 292 | 316 | -1.68% | 1,217 | 0.24 | Village |
| Bath | 6 | 256 | 275 | -1.54% | 701 | 0.36 | Village |
| Kilbourne | 7 | 250 | 267 | -1.19% | 281 | 0.89 | Village |
| Forest City | 8 | 203 | 217 | -1.46% | 388 | 0.52 | Village |
| Goofy Ridge | 9 | 172 | 238 | -6.52% | 128 | 1.35 | CDP |
| Topeka | 10 | 53 | 58 | -1.85% | 387 | 0.14 | Village |
Havana is the largest city in Mason County, with a population of 2,741.
Topeka is the smallest city in Mason County.
There are 10 cities in Mason County, Illinois.