| Name of the place | CERL ID of a place | Country | Longitude | Latitude | |
|---|---|---|---|---|---|
| Oederan | cnl00025000 | Germany | — | — | |
| Oegstgeest | cnl00016324 | Netherlands | 4.46666666666667 | 52.1830555555556 | |
| Oehringen | cnl00032829 | Germany | 9.5 | 49.2 | |
| Oettingen | cnl00012469 | Germany | 10.6 | 48.95 | |
| Ofen | cnl00012470 | Germany | 10.58 | 47.7 | |
| Offenbach | cnl00019774 | Germany | 8.76972222222222 | 50.1 | |
| Offenbach am Main (Hessen) | cnl00019774 | Germany | 8.76972222222222 | 50.1 | |
| Offwell (Devon) | cnl00024299 | England | -3.143 | 50.791 | |
| Ohladowka | cnl00019901 | Poland | 28.483333 | 49.233333 | |
| Ohlau | cnl00031524 | Germany | 17.3 | 50.933333 | |
| Oirschot | cnl00041802 | Netherlands | 5.31388888888889 | 51.505 | |
| Oisemont | cnl00021811 | France | 1.7672 | 49.9561 | |
| Oker am Hartz | cnl00021027 | — | — | — | |
| Olantigh (Kent) | cnl00024435 | England | 0.9466 | 51.1984 | |
| Oldenburg | cnl00001086 | Germany | — | — | |
| Oliva | cnl00000179 | Spain | -1.46666666666667 | 42.3716666666667 | |
| Olot | cnl00033632 | Spain | — | — | |
| Omagh (co. Tyrone) | — | Ireland | -7.309 | 54.598 | |
| Oneglia | cnl00020896 | Italy | — | — | |
| Oostende | cnl00012570 | Belgium | 2.92 | 51.22 | |
| Oosterbeek | cnl00020881 | Netherlands | — | — | |
| Oosterholt | cnl00025158 | Netherlands | 4.866667 | 51.633333 | |
| Oostzaan | cnl00025369 | Netherlands | — | — | |
| Ootmarsum | cnl00016327 | Netherlands | 6.9 | 52.41 | |
| Opatów | cnl00006471 | Poland | 21.4166666666667 | 50.7997222222222 |