| Code postal | Commune | Population |
|---|---|---|
| 59570 | Obies | 716 |
| 59680 | Obrechies | 271 |
| 59670 | Ochtezeele | 358 |
| 59970 | Odomez | 926 |
| 59132 | Ohain | 1 325 |
| 59195 | Oisy | 591 |
| 59264 | Onnaing | 8 778 |
| 59122 | Oost-Cappel | 526 |
| 59310 | Orchies | 8 368 |
| 59360 | Ors | 673 |
| 59530 | Orsinval | 551 |
| 59162 | Ostricourt | 5 288 |
| 59670 | Oudezeele | 677 |
| 59670 | Oxelaëre | 535 |