| Ruislip Woods National Nature Reserve | 307.79 ha | | — |
| Harmondsworth Moor British Airways | 132.82 ha | | — |
| Stockley Country Park Stockley Park Golf Club on behalf of Hillingdon Borough Council | 102.69 ha | | — |
| Cranford Country Park Hillingdon Council | 52.41 ha | | — |
| Yeading Brook Meadows | 52.3 ha | | — |
| Minet Country Park | 50.02 ha | | — |
| Frays Farm Meadows London Wildlife Trust | 38.02 ha | | — |
| Lake Farm Country Park | 27.33 ha | | — |
| Hillingdon Court Park | 22.39 ha | | — |
| Heathrow Colne Valley Biodiversity Site | 15.15 ha | | — |
| Broadwater Lake Nature Reserve | 15.05 ha | | — |
| Frays Island & Mabey's Meadow Nature Reserve London Wildlife Trust | 13.83 ha | | — |
| Dowding Park Hillingdon Council | 13.37 ha | | — |
| Bridgwater Road Fields | 11.81 ha | | — |
| Hale Field Park London Borough of Hillingdon | 10.68 ha | | — |
| Harefield Place Nature Reserve Hillingdon Natural History Society | 10.03 ha | | — |
| Denham Lock Wood London Wildlife Trust | 9.68 ha | | — |
| Two Bridges | 9.62 ha | | — |
| Barra Hall Park | 9.61 ha | | — |
| The Closes Recreation Ground | 9.48 ha | | — |
| Old Park Wood Nature Reserve | 8.31 ha | | — |
| Hayes End Community Park | 7.88 ha | | — |
| Bessingby Playing Fields | 7.07 ha | | — |
| Cowley Recreation Ground | 6.43 ha | | — |
| Haydon Hall Park | 5.94 ha | | — |
| Uxbridge Common | 5.58 ha | | — |
| Swakeleys Park | 5.14 ha | | — |
| Heathrow Colne Valley Biodiversity Site | 4.93 ha | | — |
| Ten Acres | 4.69 ha | | — |
| Hog's Back Open Space | 4.64 ha | | — |
| Warrender Park | 4.61 ha | | — |
| Long Meadow | 4.37 ha | | — |
| Willow Tree Open Space | 4.23 ha | | — |
| Uxbridge Alderglade | 4.2 ha | | — |
| Brook Common | 4.04 ha | | — |
| Eastcote House Gardens | 3.95 ha | | — |
| Belfry Avenue Open Space | 3.79 ha | | — |
| Coney Green | 3.71 ha | | — |
| Pinkwell Park | 3.53 ha | | — |
| Fassnidge Park | 3.17 ha | | — |
| Bolton's Lane Open Space | 3.11 ha | | — |
| Crane Meadows Hillingdon Council | 2.87 ha | | — |
| Dean Park | 2.79 ha | | — |
| Rosedale Park | 2.72 ha | | — |
| Colne Valley Biodiversity Site | 2.36 ha | | — |
| Connaught Recreation Ground Hillingdon Council | 2.19 ha | | — |
| The Grove Nature Reserve London Wildlife Trust | 2.16 ha | | — |
| Catlin's Lane Open Space | 2.13 ha | | — |
| Moorhall Recreation Ground | 1.99 ha | | — |
| Colne Valley Biodiversity Site | 1.94 ha | | — |
| Manor Farm | 1.75 ha | | — |
| Park Road Green | 1.72 ha | | — |
| William Byrd Park | 1.7 ha | | — |
| Harefield Village Green | 1.69 ha | | — |
| Berkeley Meadows | 1.6 ha | | — |
| Botanic Gardens | 1.47 ha | | — |
| Dews Farm Sand Pits | 1.43 ha | | — |
| Shenley Park | 1.35 ha | | — |
| Raisins Hill Open Space | 1.31 ha | | — |
| Frithwood Park | 1.29 ha | | — |
| The Park | 1.25 ha | | — |
| Warrren Park | 1.25 ha | | — |
| Brook Common | 1.24 ha | | — |
| Columbia Avenue Recreation Ground | 1.12 ha | | — |
| Church Gardens | 1.02 ha | | — |
| Knights Gardens | 0.98 ha | | — |
| Heathrow Biodiversity Site - Peggy Bedford | 0.97 ha | | — |
| Milton Court | 0.96 ha | | — |
| Paddocks | 0.95 ha | | — |
| Queens Walk Children's Playground | 0.61 ha | | — |
| Benjamin Zephaniah Square | 0.56 ha | | — |
| Bishopshalt School Ornamental Garden | 0.56 ha | | — |
| Crank Garden | 0.52 ha | | — |
| Broadhurst Gardens | 0.34 ha | | — |
| Langthorne Park | 0.31 ha | | — |
| Harefield Healing Garden | 0.23 ha | | — |
| Polish War Memorial Garden | 0.2 ha | | — |
| Enigma Square | 0.18 ha | | — |
| Spring Green | 0.17 ha | | — |
| Walled Garden | 0.16 ha | | — |
| Torcross Green | 0.07 ha | 🐕 | — |
| Churchill Road Pocket Park | 0.06 ha | | — |
| Crossway Green | 0.06 ha | | — |
| Crowe's Nest | 0.06 ha | | — |
| Fairway Triangle | 0.06 ha | | — |
| Bubridge Gardens Pocket Park | 0.03 ha | | — |
| Four Seasons Green | 0.02 ha | | — |
| Garden of Remembrance | 0.02 ha | | — |