| Site name | Country | County | Nearest town | Site type | Access | Classification (girth in metres) | 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 |
| 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 |
| Owletts (National Trust) | England | Kent | Gravesend | garden | Yes | Notable | View On Map |
| Owlpen Manor | England | Gloucestershire | Nailsworth | garden | No | Notable | View On Map |
| Owslebury | England | Hampshire | Winchester | churchyard | Yes | Ancient 5m-7m | View On Map |
| Owston Hall | England | Yorkshire - South | Doncaster | estate | No | Notable | View On Map |
| Oxenhall – Hawthorne Hill | England | Gloucestershire | Ross-on-Wye | footpath/road | Ancient 4m-5m | View On Map | |
| Oxford Botanic Garden | England | Oxfordshire | Oxford | garden | Yes | Lost, Notable | View On Map |
| Oystermouth | Wales | Glamorgan | Swansea | churchyard | Yes | Lost | View On Map |
| Paddockhurst Estate – Crawley | England | Sussex - West | Crawley | woodland | Yes | Ancient 5m-7m | View On Map |
| Padworth | England | Berkshire | Reading | churchyard | Yes | Notable | View On Map |