| Name | What | Region | Country | Lat | Long | Elev Ft. | Pop Est |
|---|
| Oaig Daya | city | Province of Ilocos Sur | Philippines | 17.1833333 | 120.45 | 36 | 40620 |
| Oalin | city | Province of Ilocos Sur | Philippines | 17.25 | 120.5166667 | 255 | 25542 |
| Obod | city | Province of Ilocos Sur | Philippines | 16.8833333 | 120.6166667 | 2624 | 5696 |
| Ocop | city | Province of Ilocos Sur | Philippines | 17.35 | 120.5666667 | 820 | 22076 |
| Ocup | city | Province of Ilocos Sur | Philippines | 17.35 | 120.5666667 | 820 | 22076 |
| Olo-Olo Norte | city | Province of Ilocos Sur | Philippines | 17.28 | 120.4502778 | 114 | 31043 |
| Olo-olo | city | Province of Ilocos Sur | Philippines | 17.28 | 120.4502778 | 114 | 31043 |
| Ora | city | Province of Ilocos Sur | Philippines | 17.6 | 120.4166667 | 16 | 72043 |
| Orence | city | Province of Ilocos Sur | Philippines | 17.4333333 | 120.5 | 82 | 45796 |
| Orense | city | Province of Ilocos Sur | Philippines | 17.4333333 | 120.5 | 82 | 45796 |
| Oribi | city | Province of Ilocos Sur | Philippines | 17.5 | 120.4166667 | 19 | 32500 |
| Ortoc | city | Province of Ilocos Sur | Philippines | 17.7833333 | 120.4833333 | 118 | 50916 |
| Oso | city | Province of Ilocos Sur | Philippines | 16.95 | 120.55 | 1056 | 12633 |
| Otol | city | Province of Ilocos Sur | Philippines | 17.6166667 | 120.3833333 | 16 | 82684 |
|
|