A/B C/D E/F G/H I/J/K L M N/O/P Q/R/S T/U V/W/Y
| NAME | COUNTY | LOCATION |
| Independence Lake Falls | Snohomish | Coal Creek Road |
| Infatuation Falls | Whatcom | Hearty Creek |
| Irene Creek Falls | Skagit | Cascade River Road |
| Iron Creek Falls | Skagit | Illabot Creek Road |
| Iron Mountain Falls | Skagit | Cumberland Road |
| Jack O'Lantern Falls | Whatcom | Ross Dam Trail |
| Jackson Falls | Skagit | Day Creek Area |
| Jagged Ridge Falls | Whatcom | Baker River Trail |
| Johannesburg Falls | Skagit | Cascade River Road |
| John Pierce Falls | Whatcom | Ross Lake Area |
| Jones Creek Falls | Whatcom | Van Zandt Area |
| Jordan Creek Falls | Skagit | Jordan Creek Area |
| Judd Cove Falls | San Juan | Orcas Island |
| Junction Falls | King | Snoqualmie Tree Farm |
| Kathryn Falls | Whatcom | Scott Paul Trail |
| Ketchum Creek Falls | Whatcom | Ross Lake Area |
| Klahanie Falls | Skagit | Baker Lake Area |
| Klinger Grotto Falls | King | Skykomish Area |
| Kulshan Falls | Whatcom | Heliotrope Ridge Trail |
| Kulshan Ridge Falls | Whatcom | Swift Creek Trail |