Note: As defined by the US Census Bureau, a city's official boundaries often extend miles beyond the city itself and may even cross county lines. As such, several thousand US cities officially exist in two or more counties (and therefore appear on multiple counties' lists of cities.)
City | Rank | 2024 Pop. | 2020 Pop. | Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ottawa | 1 | 18,721 | 18,843 | -0.17% | 1,257 | 14.9 | City |
| Streator | 2 | 12,202 | 12,470 | -0.55% | 1,668 | 7.3 | City |
| Peru | 3 | 9,733 | 9,921 | -0.48% | 939 | 10.4 | City |
| LaSalle | 4 | 9,388 | 9,563 | -0.47% | 698 | 13.5 | City |
| Mendota | 5 | 6,892 | 7,038 | -0.53% | 1,345 | 5.1 | City |
| Marseilles | 6 | 4,757 | 4,820 | -0.34% | 526 | 9.0 | City |
| Oglesby | 7 | 3,619 | 3,699 | -0.55% | 725 | 5.0 | City |
| Sheridan | 8 | 2,413 | 2,432 | -0.21% | 1,138 | 2.1 | Village |
| Seneca | 9 | 2,300 | 2,343 | -0.48% | 371 | 6.2 | Village |
| Earlville | 10 | 1,592 | 1,611 | -0.31% | 1,326 | 1.2 | City |
| North Utica | 11 | 1,337 | 1,317 | 0.38% | 387 | 3.5 | Village |
| Leland | 12 | 924 | 946 | -0.65% | 1,730 | 0.5 | Village |
| Tonica | 13 | 730 | 748 | -0.68% | 536 | 1.4 | Village |
| Grand Ridge | 14 | 508 | 516 | -0.39% | 1,100 | 0.5 | Village |
| Dayton | 15 | 492 | 475 | -0.61% | 268 | 1.8 | CDP |
| Lostant | 16 | 431 | 433 | -0.23% | 381 | 1.1 | Village |
| Naplate | 17 | 411 | 418 | -0.48% | 2,521 | 0.2 | Village |
| Ransom | 18 | 306 | 310 | -0.33% | 306 | 1.0 | Village |
| Cedar Point | 19 | 260 | 267 | -0.76% | 255 | 1.0 | Village |
| Rutland | 20 | 254 | 256 | -0.39% | 366 | 0.7 | Village |
| Serena | 21 | 240 | 137 | 7.62% | 976 | 0.2 | CDP |
| Kangley | 22 | 227 | 233 | -0.87% | 870 | 0.3 | Village |
| Troy Grove | 23 | 220 | 223 | -0.45% | 320 | 0.7 | Village |
| Wedron | 24 | 169 | 170 | 7.64% | 326 | 0.5 | CDP |
| Dana | 25 | 156 | 159 | -0.64% | 709 | 0.2 | Village |
| Leonore | 26 | 120 | 123 | -0.83% | 1,348 | 0.1 | Village |
| Triumph | 27 | 99 | 82 | 7.61% | 664 | 0.1 | CDP |
Note: City markers shown outside the county boundary mean that a part of the city extends into this county, but is primarily located in an adjacent county.
Ottawa is the largest city in LaSalle County.
Triumph is the smallest city in LaSalle County.
There are 27 cities in LaSalle County, Illinois.