| Cottage Construction Company | John Jacob Wrigley | — | (707) 268 1116 | GC, remodel, ADU | Bayside · Humboldt County | — | — |
| Cottage Realty | Cottage Realty | kyra@cottage-realty.com | (707) 839-1897 | Property managers | Mckinleyville · Humboldt County | — | — |
| Craftsman 316 LLC | Misha Daniel Dreckmeyr | — | (707) 613 9731 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Craig's Construction | Craig Alan Mayberry | — | (707) 834 0890 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Crawford Construction Specialties | Bryan Joshua Crawford | — | (707) 382 2854 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Crawley Construction | Richard Todd Jr Crawley | — | (707) 496 1540 | GC, remodel, ADU | Hydesville · Humboldt County | — | — |
| Creative Home Construction | William Dennis Hole | — | (707) 834 1898 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Crestmark Millwork | Scott David Olsen | info@crestmarkmillwork.com | (707) 822 4034 | Other | Arcata · Humboldt County | — | — |
| Cruz Flooring | Cruz Flooring | — | (707) 834 6446 | Other | Hydesville · Humboldt County | — | — |
| Curb Appeal Construction | Blaine David O'shaughnessy | — | (707) 267 7616 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Curtin Builder | Curtin Builder | — | (707) 502 5063 | GC, remodel, ADU | Arcata · Humboldt County | — | — |
| Curtis Daniel Brown | Curtis Daniel Brown | — | (707) 498 8868 | Windows, patio, painters | Mc Kinleyville · Humboldt County | — | — |
| Custom Structures | Custom Structures | — | (707) 599 5340 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Custom Stump Grinders | Custom Stump Grinders | customstumpgrinders@gmail.com | (707) 668 5682 | Tree | Eureka · Humboldt County | — | — |
| Custom Woodwork & Design | Aria Hart Cox | — | (707) 845 0964 | Other | Kneeland · Humboldt County | — | — |
| Cutting Edge Tree Service And Solutions | Erik Warren Tjossem | — | (707) 601 8169 | Tree | Eureka · Humboldt County | — | — |
| Cw Landscaping | Cw Landscaping | — | (707) 496 1091 | Windows, patio, painters | Rio Dell · Humboldt County | — | — |
| D B Builder | D B Builder | — | (707) 498 9630 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| D C I Builders | Dennis Bruce Del Biaggio | — | (707) 786 5450 | GC, remodel, ADU | Ferndale · Humboldt County | — | — |
| D C Mechanical | D C Mechanical | — | (707) 599 5439 | HVAC | Cutten · Humboldt County | — | — |
| D J Gallagher Construction | Daniel James Gallagher | — | (707) 616 8833 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| D R Electric INC | Donald Patrick Rasmussen | — | (707) 267 6799 | Electricians | Mc Kinleyville · Humboldt County | — | — |
| D S Construction | Duane William Brown | — | (707) 599 6778 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| D W Excavation | D W Excavation | — | (707) 601 9091 | Other | Ferndale · Humboldt County | — | — |
| Dalton General Engineering | Dalton General Engineering | — | (707) 601 2131 | Other | Mc Kinleyville · Humboldt County | — | — |
| Damon Brown | Damon Brown | — | (530) 629 3702 | Other | Willow Creek · Humboldt County | — | — |
| Dan - Kenzie Construction | Frank Silveira Gonsalves | — | (707) 407 7901 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Dan - Kenzie Construction LLC | Frank Silveira Gonsalves | — | (707) 407 7901 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Dan Birnie Construction | Daniel Robert Birnie | — | (707) 839 8660 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Dan R Nored Drywall | Dan R Nored Drywall | — | (707) 496 8066 | Other | Blue Lake · Humboldt County | — | — |
| Dan Roche Construction | Daniel Johnathon Roche | — | (707) 599 5001 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Danco Builders | Daniel James Johnson | — | (707) 822 9000 | GC, remodel, ADU | Arcata · Humboldt County | — | — |
| Danco Builders Northwest | Daniel James Johnson | — | (707) 822 9000 | GC, remodel, ADU | Arcata · Humboldt County | — | — |
| Daniel Janney | Daniel Janney | — | (707) 496 0055 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Daniel R Weeks General Building Contractor | Daniel Robert Weeks | — | (707) 407 9639 | GC, remodel, ADU | Kneeland · Humboldt County | — | — |
| Danielson Construction INC | Steven Thomas Danielson | — | (707) 444 2948 | Other | Eureka · Humboldt County | — | — |
| Dann Brauning Construction | Dann Douglas Brauning | — | (707) 839 1237 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Danner Gonsalves Construction | Danner Clin Gonsalves | — | (707) 496 2723 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Darin Thomsen Construction | Darin Scott Thomsen | — | (707) 499 0770 | GC, remodel, ADU | Loleta · Humboldt County | — | — |
| Daron Luster | Daron Luster | — | (707) 407 7000 | GC, remodel, ADU | Ferndale · Humboldt County | — | — |