| City | County | 2026 Pop. ↓ |
|---|---|---|
| Kankakee | Kankakee County | 23,267 |
| Kewanee | Henry County | 12,036 |
| Kildeer | Lake County | 4,796 |
| Knoxville | Knox County | 2,790 |
| Kenilworth | Cook County | 2,420 |
| Knollwood | Lake County | 1,944 |
| Kirkland | DeKalb County | 1,624 |
| Kincaid | Christian County | 1,301 |
| Kingston | DeKalb County | 1,099 |
| Kinmundy | Marion County | 696 |
| Kansas | Edgar County | 642 |
| Kirkwood | Warren County | 642 |
| Keithsburg | Mercer County | 545 |
| Kaneville | Kane County | 445 |
| Keyesport | Clinton County | 403 |
| Kings | DeKalb County | 396 |
| Karnak | Pulaski County | 388 |
| Kenney | De Witt County | 296 |
| Kampsville | Calhoun County | 292 |
| Kane | Greene County | 270 |
| Kingston Mines | Peoria County | 257 |
| Kilbourne | Mason County | 253 |
| Kingston | DeKalb County | 242 |
| Kappa | McLean County | 230 |
| Kangley | LaSalle County | 223 |
| Kinderhook | Pike County | 187 |
| Kempton | Ford County | 175 |
| Keensburg | Wabash County | 169 |
| Kell | Marion County | 167 |
| Kinsman | Grundy County | 91 |
| Keenes | Wayne County | 47 |
| Kaskaskia | Randolph County | 22 |