27 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ottawa | 1 | 18,691 | 18,843 | -0.16% | 1,255 | 14.89 | City |
| Streator | 2 | 12,135 | 12,470 | -0.55% | 1,659 | 7.32 | City |
| Peru | 3 | 9,686 | 9,921 | -0.48% | 934 | 10.37 | City |
| LaSalle | 4 | 9,344 | 9,563 | -0.47% | 694 | 13.46 | City |
| Mendota | 5 | 6,856 | 7,038 | -0.52% | 1,337 | 5.13 | City |
| Marseilles | 6 | 4,741 | 4,820 | -0.34% | 524 | 9.05 | City |
| Oglesby | 7 | 3,599 | 3,699 | -0.55% | 721 | 4.99 | City |
| Sheridan | 8 | 2,408 | 2,432 | -0.21% | 1,135 | 2.12 | Village |
| Seneca | 9 | 2,289 | 2,343 | -0.48% | 369 | 6.21 | Village |
| Earlville | 10 | 1,587 | 1,611 | -0.31% | 1,321 | 1.20 | City |
| North Utica | 11 | 1,342 | 1,317 | 0.37% | 388 | 3.46 | Village |
| Leland | 12 | 919 | 946 | -0.54% | 1,721 | 0.53 | Village |
| Tonica | 13 | 726 | 748 | -0.55% | 533 | 1.36 | Village |
| Grand Ridge | 14 | 506 | 516 | -0.39% | 1,095 | 0.46 | Village |
| Dayton | 15 | 488 | 475 | -0.81% | 265 | 1.84 | CDP |
| Lostant | 16 | 431 | 433 | 0% | 381 | 1.13 | Village |
| Naplate | 17 | 409 | 418 | -0.49% | 2,509 | 0.16 | Village |
| Ransom | 18 | 305 | 310 | -0.33% | 305 | 1 | Village |
| Cedar Point | 19 | 258 | 267 | -0.77% | 253 | 1.02 | Village |
| Serena | 20 | 258 | 137 | 7.5% | 1,049 | 0.25 | CDP |
| Rutland | 21 | 254 | 256 | 0% | 366 | 0.69 | Village |
| Kangley | 22 | 226 | 233 | -0.44% | 866 | 0.26 | Village |
| Troy Grove | 23 | 219 | 223 | -0.46% | 319 | 0.69 | Village |
| Wedron | 24 | 181 | 170 | 7.1% | 349 | 0.52 | CDP |
| Dana | 25 | 155 | 159 | -0.64% | 705 | 0.22 | Village |
| Leonore | 26 | 119 | 123 | -0.83% | 1,337 | 0.09 | Village |
| Triumph | 27 | 106 | 82 | 7.07% | 711 | 0.15 | CDP |
Ottawa is the largest city in LaSalle County, with a population of 18,691.
Triumph is the smallest city in LaSalle County.
There are 27 cities in LaSalle County, Illinois.