- Silvercrest Mobile Home Park
- Silverdale
- Silverdale Mobile Estates
- Silver Lake
- Silverton
- Similk Beach
- Sims Corner
- Sinclair Island
- Sine
- Sisco
- Sisco Heights
- Sixprong
- Skagit City
- Skagit Island
- Skagit Valley
- Skagit Valley View Mobile Home Park
- Skamania
- Skamania Island
- Skamokawa
- Skamokawa Valley
- Skipjack Island
- Skiyou Island
- Skokomish
- Skookumchuck
- Skull Island
- Skull Island
- Skull Rock
- Skunk Island
- Skykomish
- Skylark Village II Mobile Home Park