- Carnadero
- Carnazzani Island (historical)
- Carnelian Bay
- Carnelian Heights
- Carpenter Place
- Carpintería
- Carquinez Heights
- Carr
- Carrick
- Carrolton
- Carson
- Carson Hill
- Cartago
- Caruthers
- Carvin Creek Homesites
- Casa Conejo
- Casa de Oro
- Casa de Oro-Mount Helix
- Casa Loma
- Casa Loma
- Casa Mia Mobile Home Park
- Cascade
- Cascade Shores
- Cascade Sun Mobile Home Estates
- Cascadel Woods
- Casey Corner
- Casitas Mobile Home Park
- Casitas Springs
- Casket Rock
- Casmalia