| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Havana | 1 | 2,765 | 2,951 | -1.21% | 996 | 3 | City |
| Mason City | 2 | 1,931 | 2,068 | -1.28% | 1,906 | 1 | City |
| Manito | 3 | 1,456 | 1,549 | -1.15% | 962 | 2 | Village |
| San Jose | 4 | 455 | 480 | -1.09% | 1,099 | 0 | Village |
| Easton | 5 | 294 | 317 | -1.34% | 1,225 | 0 | Village |
| Bath | 6 | 259 | 273 | -1.15% | 710 | 0 | Village |
| Kilbourne | 7 | 253 | 267 | -1.17% | 285 | 1 | Village |
| Forest City | 8 | 209 | 220 | -0.95% | 400 | 1 | Village |
| Topeka | 9 | 49 | 53 | -2% | 358 | 0 | Village |
Havana is the largest city in Mason County, with a population of 2,765.
Topeka is the smallest city in Mason County, with a population of 49.
There are 9 cities in Mason County, Illinois.