| Site name | Country | County | Nearest town | Site type | Access | Classification (girth in metres) | View on map |
|---|---|---|---|---|---|---|---|
| Silian | Wales | Ceredigion | Lampeter | churchyard | Yes | Ancient 7m+ | View On Map |
| Silver Springs Hotel – Tivoli | Ireland | Co. Cork | Cork | garden | Yes | Ancient 4m-5m | View On Map |
| Silverton | England | Devon | Tiverton | churchyard | Yes | Ancient 7m+ | View On Map |
| Silvington – High Lane | England | Shropshire | Cleobury Mortimer | footpath/road | Yes | Ancient 4m-5m, Ancient 5m-7m, Notable | View On Map |
| Silwood Park | England | Berkshire | Bracknell | parkland | No | Notable | View On Map |
| Simmonscourt Castle | Ireland | Co. Dublin | Dublin | historic site | Yes | Notable | View On Map |
| Sizergh – Holeslack Wood | England | Cumbria | Kendal | woodland | Yes | Ancient 5m-7m, Ancient 7m+, LostNotable | View On Map |
| Skenfrith | Wales | Monmouthshire | Monmouth | churchyard | Yes | Ancient 4m-5m | View On Map |
| Skilgate | England | Somerset | Dulverton | churchyard | Yes | Ancient 4m-5m | View On Map |
| Skipton Castle | England | Yorkshire - North | Skipton | castle | Yes | Notable | View On Map |
| Slaugham | England | Sussex - West | Horsham | churchyard | Yes | Ancient 7m+, Notable | View On Map |
| Slebech | Wales | Pembrokeshire | Haverfordwest | churchyard | Yes | Lost | View On Map |
| Slimbridge | England | Gloucestershire | Gloucester | garden | No | Ancient 5m-7m | View On Map |
| Slindon Estate – West Sussex | England | Sussex - West | Chichester | woodland | Yes | Ancient 4m-5m, Notable | View On Map |
| Smalley | England | Derbyshire | Derby | churchyard | Yes | Ancient 4m-5m | View On Map |
| Smisby | England | Derbyshire | Ashby de la Zouche | churchyard | Yes | Ancient 4m-5m | View On Map |
| Snave | England | Kent | Ashford | churchyard | Yes | Lost | View On Map |
| Snead | England | Shropshire | Bishop's Castle | churchyard | Yes | Notable | View On Map |
| Snelston | England | Derbyshire | Ashbourne | churchyard | Yes | Notable | View On Map |
| Snitterfield | England | Warwickshire | Stratford-upon-Avon | churchyard | Yes | Lost | View On Map |