19 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Itasca | DuPage County | 9,488 |
| Island Lake | Lake County | 8,081 |
| Inverness | Cook County | 7,344 |
| Indian Head Park | Cook County | 3,905 |
| Ingalls Park | Will County | 2,891 |
| Ina | Jefferson County | 1,647 |
| Illiopolis | Sangamon County | 829 |
| Irvington | Washington County | 558 |
| Indian Creek | Lake County | 536 |
| Iuka | Marion County | 481 |
| Ipava | Fulton County | 418 |
| Industry | McDonough County | 383 |
| Irving | Montgomery County | 358 |
| Ivesdale | Champaign County | 261 |
| Indianola | Vermilion County | 215 |
| Iroquois | Iroquois County | 129 |
| Iola | Clay County | 94 |
| Irwin | Kankakee County | 66 |
| Illinois City | Rock Island County | 22 |