| Heartwood Forest Woodland Trust | 349.68 ha | | — |
| Gorhambury Park and Gardens The Gorhambury Estate | 240.67 ha | | — |
| Harpenden Common | 93.94 ha | | — |
| Verulamium Park | 60.9 ha | | — |
| Highfield Park | 28.22 ha | | — |
| Jersey Farm Woodland Park St Albans | 27.45 ha | | — |
| Rothamsted Park | 22.51 ha | | — |
| Kinsbourne Green Common | 19.06 ha | | — |
| Redbourn Common | 16.52 ha | | — |
| Colney Heath Common | 12.73 ha | | — |
| Clarence Park | 10.45 ha | | — |
| The Woods | 8.91 ha | | — |
| Greenwood Park | 8.81 ha | | — |
| Batford Springs Local Nature Reserve | 8.46 ha | | — |
| Former Abbey View Golf Course | 7.57 ha | | — |
| Colney Heath Common | 6.2 ha | | — |
| Wick Local Nature Reserve | 4.59 ha | | — |
| Longacres Open Space | 4.28 ha | | — |
| St Stephen's Park | 2.31 ha | | — |
| How Wood | 1.92 ha | | — |
| Stocking Springs | 1.86 ha | | — |
| St Michael's Manor Garden | 1.7 ha | | — |
| Porters Hill Park Harpenden Town Council | 1.49 ha | | — |
| Fleetville Park | 1.3 ha | | — |
| The Old Brickie | 1.04 ha | | — |
| Roestock Park | 1.03 ha | | — |
| Lydekker Park | 0.99 ha | | — |
| Melissa Field | 0.99 ha | | — |
| Townsend Bowls & Tennis Club | 0.83 ha | | — |
| Watercress Wildlife Association | 0.83 ha | | — |
| Hill End Garden of Rest | 0.75 ha | | — |
| St Leonard's Open Space Sandridge Parish Council | 0.61 ha | | — |
| Colney Heath Community Park | 0.6 ha | | — |
| Crabtree Fields | 0.6 ha | | — |
| Romeland Garden | 0.32 ha | | — |
| Vintry Garden | 0.27 ha | | — |
| Crinkle Crankle Community Garden Wheathampstead Parish Council | 0.12 ha | | — |
| The Garden of Hope | 0.11 ha | | — |
| Diamond Jubilee Garden | 0.06 ha | | — |
| Quaker Garden St Albans City and District Council | 0.05 ha | | — |
| Marsh | 0.02 ha | | — |
| Broad Colney Lakes Nature Reserve | — | | — |
| Franklin Close Amenity Garden | — | | — |