| Carnation Milk Products | Chehalis | WA |
| Carnation Milk Products | Spokane | WA |
| Carstens Packing | Spokane | WA |
| Cascade Kraft | Attalia | WA |
| Cascade Kraft | Wallula | WA |
| Casco | Olympia | WA |
| Cedar Hills Alcoholic Rehabilitation Center | Maple Valley | WA |
| Centennial Mill | Seattle | WA |
| Centralia Generation Station | Centralia | WA |
| Central Kitsap Fire & Rescue 6-4 | Bremerton | WA |
| Central Park School | Aberdeen | WA |
| Central Steam Plant | Spokane | WA |
| Central Washington College Of Education | Ellensburg | WA |
| Central Washington State College | Ellensburg | WA |
| Central Washington University | Ellensburg | WA |
| Century 21 Exposition | Seattle | WA |
| Charles R. McCormick Lumber | Port Ludlow | WA |
| Chas. D. West & Company | Tacoma | WA |
| Chef-Reddy Food | Othello | WA |
| Chelan Courthouse | Wenatchee | WA |
| Chemco | Seattle | WA |
| Chemithon | Seattle | WA |
| Chet's Wire Rope | Chehalis | WA |
| Chevron | Seattle | WA |
| Chevron | Kennewick | WA |
| Chief Reddy | Othello | WA |
| Chief Tonasket Growers | Tonasket | WA |
| Chinook Hotel | Yakima | WA |
| Church Grape Juice | Kennewick | WA |
| City Church | Issaquah | WA |
| City Sewage Treatment | Vancouver | WA |
| Claussen Brewing | Seattle | WA |
| Clear Lake Lumber | Clear Lake | WA |
| Cleveland High School | Seattle | WA |
| Clough Lumber | Seattle | WA |
| Coast Ice & Cold Storage | Everett | WA |
| Coleman Elementary School | Seattle | WA |
| Collegiana Dormitory | Seattle | WA |
| Columbia Brewers Industries | Tacoma | WA |
| Columbia Cement | Bellingham | WA |
| Columbia Clinic & Heatlh Center | Seattle | WA |
| Columbia Electric | Spokane | WA |
| Columbia Kraft | Attalia | WA |
| Columbia & Puget Sound Railway | Seattle | WA |
| Columbia Seafirst Center | Seattle | WA |
| Commencement Bay | Tacoma | WA |
| ConocoPhillips | Ferndale | WA |
| Consumers Central Heating | Tacoma | WA |
| Container Company Of America | Tacoma | WA |
| Container Company Of America | Seattle | WA |
