21 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Havana | 1 | 4,172 | 4,384 | -0.41% | 72 | 58 | Township |
| Havana | 2 | 2,762 | 2,953 | -1.15% | 995 | 3 | City |
| Mason City | 3 | 2,211 | 2,326 | -0.45% | 62 | 35 | Township |
| Manito | 4 | 2,140 | 2,239 | -0.28% | 49 | 44 | Township |
| Mason City | 5 | 1,939 | 2,068 | -1.07% | 1,914 | 1 | City |
| Manito | 6 | 1,456 | 1,552 | -1.09% | 962 | 2 | Village |
| Bath | 7 | 706 | 737 | -0.28% | 11 | 67 | Township |
| Quiver | 8 | 687 | 716 | -0.29% | 16 | 42 | Township |
| San Jose | 9 | 461 | 485 | -0.86% | 1,114 | 0 | Village |
| Forest City | 10 | 449 | 466 | -0.22% | 13 | 33 | Township |
| Kilbourne | 11 | 448 | 471 | -0.67% | 11 | 40 | Township |
| Allens Grove | 12 | 446 | 464 | 0% | 12 | 36 | Township |
| Easton | 13 | 295 | 315 | -1.01% | 1,229 | 0 | Village |
| Bath | 14 | 260 | 275 | -0.76% | 712 | 0 | Village |
| Kilbourne | 15 | 254 | 268 | -0.78% | 286 | 1 | Village |
| Lynchburg | 16 | 221 | 231 | -0.45% | 5 | 42 | Township |
| Salt Creek | 17 | 210 | 220 | -0.47% | 6 | 36 | Township |
| Forest City | 18 | 206 | 218 | -0.96% | 394 | 1 | Village |
| Pennsylvania | 19 | 150 | 156 | 0% | 4 | 36 | Township |
| Crane Creek | 20 | 149 | 155 | 0% | 4 | 34 | Township |
| Topeka | 21 | 55 | 58 | 0% | 401 | 0 | Village |
Havana is the largest city in Mason County, with a population of 4,172.
Topeka is the smallest city in Mason County, with a population of 55.
There are 21 cities in Mason County, Illinois.