Identifiers: city · village · CDP
| Rank | Community | Population |
|---|---|---|
| 1 | Ottawa (city), IL | 18,840 |
| 2 | Peru (city), IL | 9,896 |
| 3 | LaSalle (city), IL | 9,582 |
| 4 | Princeton (city), IL | 7,832 |
| 5 | Mendota (city), IL | 7,061 |
| 6 | Spring Valley (city), IL | 5,582 |
| 7 | Oglesby (city), IL | 3,712 |
| 8 | De Pue (village), IL | 1,633 |
| 9 | Earlville (city), IL | 1,613 |
| 10 | Granville (village), IL | 1,359 |
| 11 | North Utica (village), IL | 1,323 |
| 12 | Ladd (village), IL | 1,263 |
| 13 | Wenona (city), IL | 974 |
| 14 | Paw Paw (village), IL | 830 |
| 15 | Hennepin (village), IL | 769 |
| 16 | Tonica (village), IL | 749 |
| 17 | La Moille (village), IL | 679 |
| 18 | Dalzell (village), IL | 663 |
| 19 | Dayton (CDP), IL | 528 |
| 20 | Mark (village), IL | 519 |