| Ingle Construction | Christopher Michael Ingle | — | (415) 342 3037 | GC, remodel, ADU | San Anselmo · Marin County | — | — |
| Ingram Custom Building | Ingram Custom Building | — | (415) 699 2307 | GC, remodel, ADU | Corte Madera · Marin County | — | — |
| Ingram Fire Protection Incorporated | Christopher Eric Ingram | — | (650) 437 6000 | GC, remodel, ADU | Corte Madera · Marin County | — | — |
| Initial Construction | Francis Robert Wallace | — | (415) 871 1472 | GC, remodel, ADU | San Anselmo · Marin County | — | — |
| Inland Contracting INC | Enrico Paul Ielmorini | — | (707) 328 7743 | GC, remodel, ADU | Nicasio · Marin County | — | — |
| Innova Construction | Alexander Abigail Rodas Diaz | — | (415) 320 5020 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Innovative Piping Systems | Innovative Piping Systems | — | (650) 387 7682 | Other | Mill Valley · Marin County | — | — |
| Inside Line Communications | Inside Line Communications | — | (415) 456 9102 | Other | Fairfax · Marin County | — | — |
| Insight Home Maintenance | David Blake Hughes | — | (415) 559 2967 | GC, remodel, ADU | Mill Valley · Marin County | — | — |
| Inspired Environments LLC | Gregor Mendieta | — | (415) 454 8000 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Installation Of Data & Telecommunications | Theresa Maria Benecchi | — | (415) 226 0020 | Other | San Rafael · Marin County | — | — |
| Installation Of Digital Transmissions INC | James Robert Mc Gowan | — | (415) 226 0020 | Other | San Rafael · Marin County | — | — |
| Integral Design | Integral Design | — | (415) 302 0698 | Other | San Rafael · Marin County | — | — |
| Integrated Landscape Services INC | Juan Ramon Jr Amador | — | (415) 378 0644 | Windows, patio, painters | Novato · Marin County | — | — |
| Integrity Construction Partners LLC | Thomas Matthew Hogan | info@integrityconstructionpartners.com | (415) 515 9018 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| Integrity Decks & Restoration General Contracting INC | Barba Refugio | — | (510) 680 5800 | GC, remodel, ADU | Sausalito · Marin County | — | — |
| Integrity Electric INC | Gerald Joseph Thompson | office.integrityelectric@gmail.com | (415) 499 8844 | Electricians | San Rafael · Marin County | — | — |
| Integrity Pipeworks | Integrity Pipeworks | — | (415) 301 1220 | Other | San Rafael · Marin County | — | — |
| Intertie Incorporated | Richard Riker Mrlik | — | (415) 567 0446 | Other | Sausalito · Marin County | — | — |
| Inverness Gardening Service INC | Gutierrez Ismael | — | (415) 663 9035 | Windows, patio, painters | Point Reyes Station · Marin County | — | — |
| Ireland Interior Systems INC | Michael Salvatore Ireland | — | (415) 671 2903 | Other | Novato · Marin County | — | — |
| Iris Aboriculture INC | Nicholas Normindan Cravedi | — | (406) 291 8744 | Other | Mill Valley · Marin County | — | — |
| Iris Landscaping INC | Nikolay Georgiev Georgiev | — | (208) 772-0740 | GC, remodel, ADU | Novato · Marin County | — | — |
| Irish Welding INC | Dennis Edward Irish | — | (415) 250 7260 | Other | Forest Knolls · Marin County | — | — |
| Iron Grip Construction INC | Andrew Santino Miranda | — | (707) 483 0504 | GC, remodel, ADU | San Anselmo · Marin County | — | — |
| Iron Mountain Sheet Metal INC | Ronald Charles Etz | — | (970) 903 3986 | Other | Novato · Marin County | — | — |
| Irwell Electric INC | Neil Anthony Halsall | irwellelectric@gmail.com | (415) 368 2173 | Electricians | Fairfax · Marin County | — | — |
| Ivan Manchip Construction INC | Ivan Lindsay Berw Manchip | — | (415) 847 0204 | GC, remodel, ADU | Mill Valley · Marin County | — | — |
| Ivanscaping | Fernandez Ivan Melendez | — | (415) 377 0799 | Windows, patio, painters | Novato · Marin County | — | — |
| Iver Holster Construction | Iver Vincent Holster | — | (415) 370 6384 | GC, remodel, ADU | Ignacio · Marin County | — | — |
| Ivolt Electric | Ivaylo Petrov Georgiev | — | (415) 324 9060 | Electricians | Greenbrae · Marin County | — | — |
| J & D Services | Robert William Trosin | — | (415) 883 3306 | GC, remodel, ADU | Novato · Marin County | — | — |
| J & R Thompson INC | Jeffrey Allen Thompson | — | (415) 892 6030 | Windows, patio, painters | Novato · Marin County | — | — |
| J A C Construction INC | Jacques A Charton | — | (415) 336 9118 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| J A Santos Flooring Services | Jose Alfredo Santos | — | (415) 479 8379 | Other | San Rafael · Marin County | — | — |
| J B Construction | Barrow Jesse | — | (415) 868 1457 | GC, remodel, ADU | Bolinas · Marin County | — | — |
| J C C Construction | Jose Cruz Castillo | — | (415) 342 4856 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| J Castillo Construction | Jorge Luis Castillo Mendez | — | (415) 948 3613 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| J Chavez General Contractor INC | Herrera Jesus Chavez | — | (415) 465 2220 | GC, remodel, ADU | San Rafael · Marin County | — | — |
| J Clark Painting | J Clark Painting | — | (510) 970 7910 | Windows, patio, painters | San Rafael · Marin County | — | — |