There are 49 cities in Illinois that start with the letter O.
City | 2024 Population |
|---|---|
| O'Fallon | 31,855 |
| Oak Brook | 8,014 |
| Oak Forest | 25,811 |
| Oak Grove | 462 |
| Oak Lawn | 54,929 |
| Oak Park | 51,282 |
| Oak Run | 694 |
| Oakbrook Terrace | 2,671 |
| Oakdale | 194 |
| Oakford | 228 |
| Oakland | 719 |
| Oakwood | 1,271 |
| Oakwood Hills | 2,048 |
| Oblong | 1,336 |
| Oconee | 137 |
| Odell | 978 |
| Odin | 901 |
| Ogden | 708 |
| Oglesby | 3,619 |
| Ohio | 458 |
| Ohlman | 107 |
| Okawville | 1,346 |
| Old Mill Creek | 161 |
| Old Ripley | 80 |
| Old Shawneetown | 107 |
| Olive Branch | 530 |
| Olivet | 115 |
| Olmsted | 266 |
| Olney | 8,452 |
| Olympia Fields | 4,470 |
| Omaha | 190 |
| Onarga | 1,268 |
| Oneida | 668 |
| Opdyke | 260 |
| Ophiem | 222 |
| Oquawka | 1,062 |
| Orangeville | 733 |
| Oreana | 847 |
| Oregon | 3,549 |
| Orient | 319 |
| Orion | 1,717 |
| Orland Hills | 6,483 |
| Orland Park | 56,584 |
| Osco | 139 |
| Oswego | 37,857 |
| Ottawa | 18,721 |
| Otterville | 82 |
| Owaneco | 205 |
| Oxville | 27 |