| #1 Quality Painting INC | Pedro Abraham Martinez | — | (415) 577 7599 | Windows, patio, painters | Richmond · Contra Costa County | — | — |
| 1 Demolition | 1 Demolition | — | (510) 229 6797 | Other | El Cerrito · Contra Costa County | — | — |
| 1 Tom Plumber Concord | Dennis Earl Debenham | — | (925) 922 0594 | Other | Concord · Contra Costa County | — | — |
| 1 Up Construction INC | Roger Arlen Mills | — | (925) 503 7024 | GC, remodel, ADU | Brentwood · Contra Costa County | — | — |
| 101 Concrete Services | Perez Humberto Rodriguez | — | (707) 344 2214 | Other | Bay Point · Contra Costa County | — | — |
| 1st Gen HVAC LLC | Fredy Jr Ruiz | — | (510) 375 9084 | HVAC | Richmond · Contra Costa County | — | — |
| 1st Streamline Construction INC | Timothy James Stevenson | — | (925) 350 1346 | GC, remodel, ADU | Oakley · Contra Costa County | — | — |
| 2 R Construction | Romero Ramon | — | (510) 367 6131 | GC, remodel, ADU | Bay Point · Contra Costa County | — | — |
| 2020 Electric INC | Hernandez Jaime Ruiz | — | (925) 305 9103 | Electricians | Oakley · Contra Costa County | — | — |
| 360 Construction J N | Jorge Arturo Navarrete Avila | — | (925) 437 1099 | GC, remodel, ADU | Pittsburg · Contra Costa County | — | — |
| 360 Floors & More INC | Brian Ross Blankenship | — | (925) 864 0578 | Other | Antioch · Contra Costa County | — | — |
| 360 Welding And Fabrication INC DBA 360 Ornamental Metal | Erjon Beqo | — | (510) 284 9734 | Other | Pinole · Contra Costa County | — | — |
| 365 Furniture Assembly | 365 Furniture Assembly | — | (415) 699 4556 | Other | Concord · Contra Costa County | — | — |
| 3D Technical Services INC | Daniel Timothy Farley | — | (925) 691 5543 | Electricians | Clayton · Contra Costa County | — | — |
| 3G Builders And Renovation | Joseph Von Edward Guthrie | — | (925) 497 0833 | GC, remodel, ADU | San Pablo · Contra Costa County | — | — |
| 3G Plumbing | 3G Plumbing | — | (510) 480 9844 | Other | San Pablo · Contra Costa County | — | — |
| 3rd Generation Painting | 3rd Generation Painting | — | (925) 382 8997 | Windows, patio, painters | Concord · Contra Costa County | — | — |
| 3rd Party Management Services LLC DBA Griffs Construction | Joshua John Griffin | — | (925) 966 4455 | GC, remodel, ADU | Martinez · Contra Costa County | — | — |
| 3vi INC | Zara Sophia Faith Younossi | — | (925) 236 0170 | Other | San Ramon · Contra Costa County | — | — |
| 4 Sons Concrete | 4 Sons Concrete | — | (925) 488 7757 | Other | San Ramon · Contra Costa County | — | — |
| 411 Heating & AC LLC | Mauluddi Said Opeyany | — | (925) 953 3007 | HVAC | Clayton · Contra Costa County | — | — |
| 5 Star Tree & Landscape | 5 Star Tree & Landscape | — | (925) 260 8901 | Windows, patio, painters | Walnut Creek · Contra Costa County | — | — |
| 500 Elite Builders LLC | Sornphet Jantharid | — | (510) 599 2102 | GC, remodel, ADU | Brentwood · Contra Costa County | — | — |
| 505 Earthworks LLC | Hayden Kaspar Item | — | (925) 808 5098 | Other | Discovery Bay · Contra Costa County | — | — |
| 55geeks | Sahar Maher Osman | — | (855) 554 3357 | Electricians | Martinez · Contra Costa County | — | — |
| 625 St Clair Development Incorporated | Timothy Hawkins | — | (510) 686 0858 | GC, remodel, ADU | Brentwood · Contra Costa County | — | — |
| 680 Home Repair.com | Jason Sangku Pak | — | (510) 364 1214 | Electricians | San Ramon · Contra Costa County | — | — |
| 680 Home Repairs | Steve Hyun Lee | — | (510) 364 1214 | Electricians | San Ramon · Contra Costa County | — | — |
| 7 Designs Iron | 7 Designs Iron | — | (916) 740 5525 | Other | Antioch · Contra Costa County | — | — |
| 8 Angels Pro Concrete | Elia Tokotuu Faupula | — | (925) 658 8842 | Other | Clayton · Contra Costa County | — | — |
| 925 Door Service | Soccol Raffaele | — | (925) 440 0504 | Other | Walnut Creek · Contra Costa County | — | — |
| 925 Flooring | 925 Flooring | — | (925) 250 6571 | Other | Concord · Contra Costa County | — | — |
| 99 North Construction & Plumbing INC | Denis Leonid Climov | — | (415) 650 6503 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| 99 North General Engineering | Denis Leonid Climov | — | (415) 650 6503 | HVAC | Concord · Contra Costa County | — | — |
| A & A Consulting Engineers | A & A Consulting Engineers | — | (510) 260 4538 | GC, remodel, ADU | Antioch · Contra Costa County | — | — |
| A & B Electric | Anthony John Belleci | — | (925) 260 9098 | Electricians | Brentwood · Contra Costa County | — | — |
| A & B Landscape Design & Maintenance INC | Pedro Arciniega Brambila | — | (925) 513 1899 | Windows, patio, painters | Brentwood · Contra Costa County | — | — |
| A & C Construction | Castaneda Arturo | — | (925) 628 6427 | GC, remodel, ADU | Bay Point · Contra Costa County | — | — |
| A & D Plumbing | A & D Plumbing | — | (925) 922 4770 | Other | Walnut Creek · Contra Costa County | — | — |
| A & F All Bay Painting INC | Alvarez Cesar Gonzalez | — | (510) 942 1470 | Windows, patio, painters | San Pablo · Contra Costa County | — | — |