| Site name | Country | County | Nearest town | Site type | Access | Classification (girth in metres) | View on map |
|---|---|---|---|---|---|---|---|
| Osmington | England | Dorset | Weymouth | churchyard | Yes | Ancient 4m-5m | View On Map |
| Ospringe | England | Kent | Faversham | churchyard | Yes | Notable | View On Map |
| Oswestry | England | Shropshire | Oswestry | churchyard | Yes | Ancient 5m-7m | View On Map |
| Oswestry – The Hayes | England | Shropshire | Oswestry | garden | No | Lost, Notable | View On Map |
| Oswestry – Welsh Walls | England | Shropshire | Oswestry | churchyard | Yes | Notable | View On Map |
| Otford | England | Kent | Sevenoaks | churchyard | Yes | Ancient 4m-5m | View On Map |
| Otham | England | Kent | Maidstone | churchyard | Yes | Lost | View On Map |
| Othery | England | Somerset | Langport | churchyard | Yes | Notable | View On Map |
| Otterbourne | England | Hampshire | Winchester | woodland | No | Ancient 4m-5m, Ancient 5m-7m | View On Map |
| Otterhampton | England | Somerset | Bridgwater | churchyard | Yes | Notable | View On Map |
| Otterston – nr Aberdour | Scotland | Fife | Dunfermline | garden | No | Ancient 4m-5m, Notable | View On Map |
| Otterton – church | England | Devon | Budleigh Salterton | churchyard | Yes | Notable | View On Map |
| Otterton – vicarage | England | Devon | Budleigh Salterton | former religious site | No | Ancient 4m-5m | View On Map |
| Ouilly le Tesson | France | Calvados - Normandie | Falaise | churchyard | Yes | Ancient 4m-5m | View On Map |
| Over | England | Cheshire | Northwich | churchyard | Yes | Notable | View On Map |
| Overbury | England | Worcestershire | Tewkesbury | churchyard | Yes | Ancient 4m-5m | View On Map |
| Overton | Wales | Wrexham | Wrexham | churchyard | Yes | Ancient 4m-5m, Ancient 5m-7m | View On Map |
| Overwater Hall | England | Cumbria | Keswick | garden | No | Notable | View On Map |
| Ovingdean | England | Sussex - East | Brighton | churchyard | Yes | Notable | View On Map |
| Ower | England | Hampshire | Southampton | garden | No | Ancient 5m-7m | View On Map |