23 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ottawa | 1 | 18,752 | 18,821 | -0.06% | 1,259 | 15 | City |
| Streator | 2 | 12,187 | 12,510 | -0.44% | 1,666 | 7 | City |
| Peru | 3 | 9,735 | 9,909 | -0.3% | 932 | 10 | City |
| LaSalle | 4 | 9,353 | 9,566 | -0.37% | 695 | 13 | City |
| Mendota | 5 | 6,863 | 7,040 | -0.42% | 1,339 | 5 | City |
| Marseilles | 6 | 4,753 | 4,830 | -0.27% | 504 | 9 | City |
| Oglesby | 7 | 3,593 | 3,692 | -0.44% | 720 | 5 | City |
| Sheridan | 8 | 2,407 | 2,424 | -0.12% | 1,135 | 2 | Village |
| Seneca | 9 | 2,292 | 2,345 | -0.39% | 385 | 6 | Village |
| Earlville | 10 | 1,591 | 1,611 | -0.19% | 1,325 | 1 | City |
| North Utica | 11 | 1,352 | 1,325 | 0.37% | 391 | 3 | Village |
| Leland | 12 | 919 | 946 | -0.43% | 1,721 | 1 | Village |
| Tonica | 13 | 730 | 748 | -0.41% | 536 | 1 | Village |
| Grand Ridge | 14 | 504 | 516 | -0.4% | 1,091 | 0 | Village |
| Lostant | 15 | 428 | 433 | -0.23% | 379 | 1 | Village |
| Naplate | 16 | 411 | 419 | -0.24% | 2,521 | 0 | Village |
| Ransom | 17 | 308 | 310 | 0% | 308 | 1 | Village |
| Cedar Point | 18 | 258 | 266 | -0.39% | 253 | 1 | Village |
| Rutland | 19 | 255 | 255 | 0% | 367 | 1 | Village |
| Kangley | 20 | 227 | 233 | -0.44% | 870 | 0 | Village |
| Troy Grove | 21 | 221 | 224 | 0% | 322 | 1 | Village |
| Dana | 22 | 156 | 159 | 0% | 709 | 0 | Village |
| Leonore | 23 | 120 | 123 | 0% | 1,348 | 0 | Village |
Ottawa is the largest city in LaSalle County, with a population of 18,752.
Leonore is the smallest city in LaSalle County, with a population of 120.
There are 23 cities in LaSalle County, Illinois.