| Sean Anderson Construction | Sean Joseph Anderson | — | (707) 601 1645 | GC, remodel, ADU | Rio Dell · Humboldt County | — | — |
| Sean Houston Construction | Sean Gilbert Houston | — | (707) 834 5153 | GC, remodel, ADU | Arcata · Humboldt County | — | — |
| Security Lock & Alarm | Security Lock & Alarm | — | (707) 443-7226 | Alarm and generators | Eureka · Humboldt County | — | — |
| Sempervirens Gardening LLC | Alvarado Sanchez Carlos | — | (707) 362 5727 | Windows, patio, painters | Arcata · Humboldt County | — | — |
| Sequoia Construction Specialties | Brian James Pritchard | — | (707) 442 3596 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Sequoia Custom Drywall | Sequoia Custom Drywall | — | (707) 616 8692 | Other | Eureka · Humboldt County | — | — |
| Sequoia Plumbing LLC | Ethan Forest Haymes | — | (707) 382 8337 | Other | Arcata · Humboldt County | — | — |
| Sergio Valencia Construction | Sergio Marcial Valencia | — | (707) 498 9722 | GC, remodel, ADU | Fortuna · Humboldt County | — | — |
| Sexton Construction | Daniel Scott Sexton | — | (707) 834 6301 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Shafers Stove Shop | Shafers Stove Shop | — | (707) 442 5734 | Other | Eureka · Humboldt County | — | — |
| Shawn Studebaker Excavation | Shawn Studebaker Excavation | — | (707) 223 0283 | Other | Redway · Humboldt County | — | — |
| Shawn Turner Construction | Shawn Lee Turner | — | (530) 515 0723 | GC, remodel, ADU | Hoopa · Humboldt County | — | — |
| Sholes Overhead Door INC | Allen Shayne Reed | — | (707) 822 3371 | Other | Blue Lake · Humboldt County | — | — |
| Shultz Construction | Nicholas Adrian Shultz | — | (707) 672 9298 | GC, remodel, ADU | Fortuna · Humboldt County | — | — |
| Silver Creek Construction | Michael Joseph Davey | — | (707) 599 2253 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Simera Masonry | Simera Masonry | — | (707) 499 7671 | Other | Fortuna · Humboldt County | — | — |
| Simple Visions INC | Louie Sonny Rodriguez | — | (707) 441 1347 | GC, remodel, ADU | Arcata · Humboldt County | — | — |
| Simpson Const | Simpson Const | — | (707) 496 6600 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Six Rivers Communications INC | Harold Ray Daniels | — | (707) 443 4448 | Other | Eureka · Humboldt County | — | — |
| Six Rivers Excavation | Six Rivers Excavation | jon@sixriversexcavation.com | (707) 599 8304 | Other | Arcata · Humboldt County | — | — |
| Six Rivers Mechanical INC | Jeffrey Allen Schafer | — | (707) 499 5867 | HVAC | Eureka · Humboldt County | — | — |
| Six Rivers Painting | Six Rivers Painting | — | (707) 499 4220 | Windows, patio, painters | Eureka · Humboldt County | — | — |
| Sjl Construction INC | Shannon Joseph Leonardo | — | (707) 682 6150 | Other | Ferndale · Humboldt County | — | — |
| Sjr Masonry & Construction | Steven Joseph Rodriguez | — | (707) 839 2103 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Skyshield Roofing | Alexis Omar Juarez | info@skyshieldcorp.com | (707) 613 7250 | Other roofers | Eureka · Humboldt County | — | — |
| Slionys Painting | Slionys Painting | — | (707) 442 2324 | Windows, patio, painters | Eureka · Humboldt County | — | — |
| Smith Construction | James Allen Smith | — | (707) 496 2376 | GC, remodel, ADU | Fortuna · Humboldt County | — | — |
| Soil Seekers Landscape | Simon Turner Trapkus | — | (707) 825 9585 | Windows, patio, painters | Arcata · Humboldt County | — | — |
| Solid Construction And Repair | Ryan David Benz | — | (707) 362 9479 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| South Bay One Lighting | South Bay One Lighting | — | (707) 442 8077 | Electricians | Eureka · Humboldt County | — | — |
| Sovereign Construction | Samuel Moses Butler | — | (707) 440 9089 | GC, remodel, ADU | Hydesville · Humboldt County | — | — |
| Spaulding Mechanical | Spaulding Mechanical | — | (707) 498 9425 | HVAC | Eureka · Humboldt County | — | — |
| Spencer Electric INC | Mark Douglas Spencer | info@spencer-electric.com | (707) 496 2996 | Electricians | Cutten · Humboldt County | — | — |
| Splash Pool & Spa | Splash Pool & Spa | — | (707) 834 8011 | Pool | Fortuna · Humboldt County | — | — |
| Springville Development Co INC | Perry Joseph Dove | — | (707) 725 6679 | GC, remodel, ADU | Fortuna · Humboldt County | — | — |
| Squatchies Trees LLC | Benjamin Russel Blackburn | — | (415) 912 7479 | Tree | Arcata · Humboldt County | — | — |
| Stainbrook Handyman Service | Jared Taylor Stainbrook | contact@sansoxygen.com | (707) 617 8855 | GC, remodel, ADU | Mc Kinleyville · Humboldt County | — | — |
| Staley Construction | Keith Edward Staley | — | (707) 845 1320 | GC, remodel, ADU | Eureka · Humboldt County | — | — |
| Stanmar Construction | Kopiej Stanislaw | — | (707) 273 9433 | GC, remodel, ADU | Fortuna · Humboldt County | — | — |
| Starr Painting LLC | Sean Farrel Starr | — | (707) 499 0648 | Windows, patio, painters | Cutten · Humboldt County | — | — |