| 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 | — | — |
| 101 Concrete Services | Perez Humberto Rodriguez | — | (707) 344 2214 | Other | Bay Point · 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 | — | — |
| 3G Plumbing | 3G Plumbing | — | (510) 480 9844 | Other | San Pablo · 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 | — | — |
| 505 Earthworks LLC | Hayden Kaspar Item | — | (925) 808 5098 | Other | Discovery Bay · 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 | — | — |
| A & D Plumbing | A & D Plumbing | — | (925) 922 4770 | Other | Walnut Creek · Contra Costa County | — | — |
| A & G General Maintenance INC | Piceno Gricelda Gomez | — | (925) 565 5502 | Other | Antioch · Contra Costa County | — | — |
| A & G Masonry | Francisco Javier Arriaga | — | (510) 932 4652 | Other | Richmond · Contra Costa County | — | — |
| A & M Fire Protection | A & M Fire Protection | — | (510) 314 5613 | Other | Martinez · Contra Costa County | — | — |
| A & R Plumbing And Drain INC | Armin Jiovany Rios | — | (510) 609 2804 | Other | Richmond · Contra Costa County | — | — |
| A - 1 Planet Products INC | Dante Braz Queiroz | — | (510) 237 0008 | Other | Richmond · Contra Costa County | — | — |
| A Better Cabinet & Design | A Better Cabinet & Design | — | (510) 260 0590 | Other | El Cerrito · Contra Costa County | — | — |
| A D Family Plumbing Services | Vasquez Alejandro Diaz | — | (510) 512 5029 | Other | Pittsburg · Contra Costa County | — | — |
| A D Hauling | A D Hauling | — | (510) 914 3740 | Other | Richmond · Contra Costa County | — | — |
| A D L Professional Insulation | Adolfo Daniel Luperdi | — | (408) 771 6324 | Other | Antioch · Contra Costa County | — | — |
| A E Flooring | A E Flooring | — | (661) 964 8585 | Other | Canyon · Contra Costa County | — | — |
| A G Construction | Jose Antonio Godinez | — | (510) 750 8234 | Other | Richmond · Contra Costa County | — | — |
| A G Drywall | A G Drywall | — | (813) 388-7563 | Other | Pacheco · Contra Costa County | — | — |
| A G Pavers | Anselmo Antonio Goulart | — | (925) 327 0804 | Other | San Ramon · Contra Costa County | — | — |
| A L Hardwood Floors | A L Hardwood Floors | — | (925) 943 1107 | Other | Walnut Creek · Contra Costa County | — | — |
| A O Jones Paving INC | John Larry Jones | anapbm@gmail.com | (925) 439 7027 | Other | Pittsburg · Contra Costa County | — | — |
| A Plus Plumbing | A Plus Plumbing | aplusplumbingser@gmail.com | (925) 383 8499 | Other | Discovery Bay · Contra Costa County | — | — |
| A R G Mobile Welding | A R G Mobile Welding | argwelding1@gmail.com | (510) 253 9133 | Other | Richmond · Contra Costa County | — | — |
| A S T Installations | A S T Installations | — | (415) 424 8094 | Other | Oakley · Contra Costa County | — | — |
| A T S Communications INC | Thomas Paul Klosterman | — | (925) 602 1500 | Other | Concord · Contra Costa County | — | — |
| A V Structural INC DBA A V Company | Katheryn Vykhanhtrong Nguyen | — | (415) 386 8086 | Other | Concord · Contra Costa County | — | — |
| A-1 Fire Protection Services INC | Doyle Delon Muhammad | — | (925) 305 5884 | Other | Oakley · Contra Costa County | — | — |
| A-s Pipelines INC | John Paul Arcidiacono | — | (925) 671 7711 | Other | Concord · Contra Costa County | — | — |
| A-z Plumbing INC | Vladimir Reese | — | (925) 399 7779 | Other | Oakley · Contra Costa County | — | — |
| A1 Quality Refinishing | A1 Quality Refinishing | info@a1qualityrefinishing.com | (925) 798 1144 | Other | Danville · Contra Costa County | — | — |
| A5 Floors INC | Jose Alfredo Palmer-gonzalez | — | (510) 472 5568 | Other | Antioch · Contra Costa County | — | — |