| Cascade Christian Academy | Wenatchee | Private school | K–12 | 0 |
| Cascade Christian -junior High/high School | Puyallup | Private school | 7–12 | 0 |
| Cascade Christian - Puyallup Elementary | Puyallup | Private school | K–6 | 0 |
| Cascade Christian School - McAlder Elementary | Puyallup | Private school | K–6 | 0 |
| Cascade Christian Schools - Frederickson Elem. | Tacoma | Private school | K–6 | 0 |
| Cascade Vista Baptist School | Kent | Private school | K–12 | 0 |
| Cascades Montessori Middle | Bellingham | Private school | 7–8 | 0 |
| Cascadia School | Redmond | Private school | K–5 | 0 |
| Cascadia School | Vancouver | Private school | 1–8 | 0 |
| Cataldo Catholic School | Spokane | Private school | PK–8 | 0 |
| Cedar Crest Academy | Redmond | Private school | PK–K | 0 |
| Cedar Crest Academy Bellewood | Bellevue | Private school | PK–5 | 0 |
| Cedar Crest Academy - Bellewood Campus | Bellevue | Private school | K–5 | 0 |
| Cedar Crest Academy Kirkland | Kirkland | Private school | PK–K | 0 |
| Cedar Park Christian School-lynnwood Campus | Lynnwood | Private school | PK–5 | 0 |
| Cedar River Montessori School | Renton | Private school | PK–8 | 0 |
| Cedar Tree Classical Christian School | Ridgefield | Private school | K–12 | 0 |
| Cedar Tree Montessori | Bellingham | Private school | PK–6 | 0 |
| Cedarbrook Adventist Christian | Port Hadlock | Private school | 2–8 | 0 |
| Central Kitsap Montessori | Poulsbo | Private school | PK–K | 0 |
| Centralia Christian School | Centralia | Private school | PK–10 | 0 |
| Charles Wright Academy | Tacoma | Private school | PK–12 | 0 |
| Chesterton Academy Of Notre Dame | Spokane | Private school | 9–12 | 0 |
| Chestnut Hill Academy | Bellevue | Private school | K–5 | 0 |
| Chestnut Montessori School | Bellevue | Private school | PK–3 | 0 |
| Children's Garden Montessori | Richland | Private school | PK–3 | 0 |
| Children's Garden Montessori School Of Poulsbo | Poulsbo | Private school | PK–K | 0 |
| Childrens Gate Montessori School | Wenatchee | Private school | PK–K | 0 |
| Childrens House Montessori | Spokane | Private school | PK–K | 0 |
| Children's Institute For Learning Differences | Renton | Private school | 2–12 | 0 |
| Christ The King Lutheran School | Bremerton | Private school | PK–8 | 0 |
| Christ The King Parish School | Seattle | Private school | PK–8 | 0 |
| Christ The King School | Richland | Private school | PK–8 | 0 |
| Christ The Teacher Catholic School | Yakima | Private school | K–8 | 0 |
| Christian Worship Center Academy | Zillah | Private school | PK–10 | 0 |
| Chrysalis Elementary School | Woodinville | Private school | K–6 | 0 |
| Chrysalis High School | Woodinville | Private school | 7–12 | 0 |
| Columbia Adventist Academy | Battle Ground | Private school | 9–12 | 0 |
| Colville Valley Junior Academy | Colville | Private school | PK–8 | 0 |
| Concordia Christian Academy | Tacoma | Private school | K–12 | 0 |
| Concordia Christian Academy | Tacoma | Private school | K–12 | 0 |
| Concordia Lutheran School | Seattle | Private school | PK–8 | 0 |
| Cornerstone Montessori School | Sumner | Private school | PK–6 | 0 |
| Countryside Montessori | Kirkland | Private school | PK–K | 0 |
| Covenant Christian School | Moses Lake | Private school | K–10 | 0 |
| Covenant Christian School | Lynden | Private school | K–8 | 0 |
| Cowlitz School At The Confuence | Packwood | Private school | 9–12 | 0 |
| Creative Learning Center Llc | Mercer Island | Private school | PK–K | 0 |
| Creative Montessori School | Kenmore | Private school | PK–K | 0 |
| Crestview Christian School | Moses Lake | Private school | K–8 | 0 |