9 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Havana | 1 | 2,762 | 2,953 | -1.15% | 995 | 3 | City |
| Mason City | 2 | 1,939 | 2,068 | -1.07% | 1,914 | 1 | City |
| Manito | 3 | 1,456 | 1,552 | -1.09% | 962 | 2 | Village |
| San Jose | 4 | 461 | 485 | -0.86% | 1,114 | 0 | Village |
| Easton | 5 | 295 | 315 | -1.01% | 1,229 | 0 | Village |
| Bath | 6 | 260 | 275 | -0.76% | 712 | 0 | Village |
| Kilbourne | 7 | 254 | 268 | -0.78% | 286 | 1 | Village |
| Forest City | 8 | 206 | 218 | -0.96% | 394 | 1 | Village |
| Topeka | 9 | 55 | 58 | 0% | 401 | 0 | Village |
Havana is the largest city in Mason County, with a population of 2,762.
Topeka is the smallest city in Mason County, with a population of 55.
There are 9 cities in Mason County, Illinois.