27 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ionia | 1 | 11,986 | 13,378 | -2.27% | 2,215 | 5 | City |
| Boston | 2 | 6,101 | 6,034 | 0.28% | 174 | 35 | Township |
| Belding | 3 | 5,972 | 5,945 | 0.08% | 1,264 | 5 | City |
| Ionia | 4 | 4,098 | 3,990 | 0.49% | 122 | 33 | Township |
| Portland | 5 | 3,958 | 3,895 | 0.33% | 123 | 32 | Township |
| Odessa | 6 | 3,942 | 3,915 | 0.13% | 111 | 36 | Township |
| Portland | 7 | 3,760 | 3,809 | -0.27% | 1,430 | 3 | City |
| Lyons | 8 | 3,556 | 3,518 | 0.23% | 99 | 36 | Township |
| Easton | 9 | 3,116 | 3,057 | 0.39% | 110 | 28 | Township |
| Danby | 10 | 2,989 | 2,956 | 0.34% | 85 | 35 | Township |
| Orleans | 11 | 2,735 | 2,672 | 0.44% | 78 | 35 | Township |
| Campbell | 12 | 2,419 | 2,399 | 0.17% | 68 | 36 | Township |
| Otisco | 13 | 2,296 | 2,276 | 0.17% | 74 | 31 | Township |
| Berlin | 14 | 2,156 | 2,139 | 0.23% | 52 | 41 | Township |
| Lake Odessa | 15 | 2,068 | 2,051 | 0.15% | 2,324 | 1 | Village |
| Ronald | 16 | 1,896 | 1,855 | 0.42% | 52 | 36 | Township |
| Keene | 17 | 1,742 | 1,728 | 0.11% | 49 | 36 | Township |
| Saranac | 18 | 1,380 | 1,375 | 0.07% | 1,200 | 1 | Village |
| North Plains | 19 | 1,199 | 1,187 | 0.25% | 34 | 36 | Township |
| Sebewa | 20 | 1,147 | 1,131 | 0.35% | 32 | 36 | Township |
| Orange | 21 | 1,028 | 1,007 | 0.29% | 29 | 36 | Township |
| Lyons | 22 | 778 | 772 | 0.13% | 639 | 1 | Village |
| Muir | 23 | 645 | 642 | 0% | 906 | 1 | Village |
| Pewamo | 24 | 517 | 515 | 0% | 517 | 1 | Village |
| Palo | 25 | 509 | 431 | 7.16% | 730 | 1 | CDP |
| Clarksville | 26 | 401 | 399 | 0% | 796 | 1 | Village |
| Hubbardston | 27 | 344 | 341 | 0% | 237 | 1 | Village |
Ionia is the largest city in Ionia County, with a population of 11,986.
Hubbardston is the smallest city in Ionia County, with a population of 344.
There are 27 cities in Ionia County, Michigan.