| William Hughes | William Hughes | — | (415) 459 4764 | Other | Fairfax · Marin County | — | — |
| William Kopiecki | William Kopiecki | — | (208) 610 1083 | GC, remodel, ADU | Novato · Marin County | — | — |
| William Lowell Hibbs Jr | William Lowell Hibbs Jr | — | (415) 264 2899 | GC, remodel, ADU | Fairfax · Marin County | — | — |
| William M Lancaster | William M Lancaster | — | (415) 755 5389 | GC, remodel, ADU | Novato · Marin County | — | — |
| William Paul Majoue | William Paul Majoue | — | (415) 601 7433 | Electricians | Pt Reyes Station · Marin County | — | — |
| William Prince Design & Building | William Prince Design & Building | — | (415) 669 7332 | GC, remodel, ADU | Inverness · Marin County | — | — |
| William Thomas Pollock | William Thomas Pollock | — | (530) 320 1439 | GC, remodel, ADU | Greenbrae · Marin County | — | — |
| William's Pleasure Island Landscape | William's Pleasure Island Landscape | — | (415) 606 6479 | Windows, patio, painters | Forest Knolls · Marin County | — | — |
| Williams Construction Co | Max Justin Williams | — | (415) 302 1348 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Willy May | Willy May | — | (415) 342 2857 | Other | San Rafael · Marin County | — | — |
| Wilson Building Company LLC | Melissa Marie Wilson | wilsonbldinc@gmail.com | (415) 952 7006 | GC, remodel, ADU | Mill Valley · Marin County | — | — |
| Wilson Construction | Connor Macleod Wilson | — | (628) 336 0332 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Wilson Electric | Paul Garett Wilson | quotes@wilsonelectric.com | (831) 331 5798 | Electricians | Fairfax · Marin County | — | — |
| Wilson's Plumbing | Wilson's Plumbing | — | (415) 457 6941 | Other | San Anselmo · Marin County | — | — |
| Wilvas Construction | Wilfredo Bernabe Vasquez Perez | — | (415) 601 5574 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Window Factory | Jaclyn Blum Guelfi | — | (415) 924 3300 | GC, remodel, ADU | Greenbrae · Marin County | — | — |
| Wingers Erection Co | Philip Leslie Ray | — | (415) 381 1206 | GC, remodel, ADU | Mill Valley · Marin County | — | — |
| Wishart Tile | Wishart Tile | — | (415) 350 4357 | Other | San Rafael · Marin County | — | — |
| Wj Rodas Construction | Wesli Hamilton Rodas Calderon | — | (415) 870 0085 | GC, remodel, ADU | Novato · Marin County | — | — |
| Wm Esteban Martinez | Wm Esteban Martinez | — | (415) 342 6652 | Windows, patio, painters | San Rafael · Marin County | — | — |
| Wolf Landscapes | Wolf Landscapes | — | (415) 453 7286 | Windows, patio, painters | Fairfax · Marin County | — | — |
| Wolfgang Buck Electric INC | Wolfgang Bernhard Buck | — | (415) 789 9727 | Electricians | Tiburon · Marin County | — | — |
| Wood Builder | Wood Builder | — | (415) 328 5924 | GC, remodel, ADU | Novato · Marin County | — | — |
| Woodacre Electric Company | Lawrence Austin Daunell | — | (415) 717 2731 | Electricians | Woodacre · Marin County | — | — |
| Woody's Fences | Woody's Fences | woodysfencesonline@gmail.com | (415) 456-0880 | Other | San Rafael · Marin County | — | — |
| Woody's Restoration Services | William Harrison Von Lackum | — | (415) 453 7500 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Wooley Landscapes | Wooley Landscapes | — | (415) 515 0194 | Windows, patio, painters | Fairfax · Marin County | — | — |
| Wormood INC | Eric Von Pein Wormood | — | (415) 518 6060 | GC, remodel, ADU | Novato · Marin County | — | — |
| Wyatt Studio INC DBA Wyatt Studio Welding | John Wyatt Ellison | — | (415) 559 9131 | Other | Novato · Marin County | — | — |
| X Y Z Electric | Bajramovic Edin | — | (415) 320 9508 | Electricians | Novato · Marin County | — | — |
| Xmag Construction | Xavier Alexander Magana | — | (415) 328 4990 | GC, remodel, ADU | Novato · Marin County | — | — |
| Yardwork Landscaping | Yardwork Landscaping | info@yardworklandscaping.com | (415) 380 8362 | Windows, patio, painters | San Rafael · Marin County | — | — |
| Yardzen Services | Adam D Messner | — | (650) 444 0458 | Windows, patio, painters | Mill Valley · Marin County | — | — |
| Yates Sherlock Construction | Yates Hamilton Sherlock | — | (415) 717 4267 | GC, remodel, ADU | Tiburon · Marin County | — | — |
| Yazy Construction | David William Esparza | — | (415) 203 6535 | GC, remodel, ADU | Fairfax · Marin County | — | — |
| Yonts Construction | Sean Gregory Yonts | — | (415) 717 7101 | GC, remodel, ADU | San Anselmo · Marin County | — | — |
| Young Brothers Remodeling INC | Sean Allan Young | youngbrothersremodeling@gmail.com | (415) 261 3595 | GC, remodel, ADU | Corte Madera · Marin County | — | — |
| Your Energy Space | Roman Zalynskii | — | (415) 638 0794 | HVAC | Sausalito · Marin County | — | — |
| Yourspace Construction | Vadim Zadara | — | (707) 625 5555 | GC, remodel, ADU | Sausalito · Marin County | — | — |
| Zak Plumbing Co | Spencer Joseph Zak | — | (415) 383 6317 | Other | Mill Valley · Marin County | — | — |