| Oakdale Roofing INC | Ricky Lee Hickman | — | (209) 537 7994 | Other roofers | Turlock · Stanislaus County | — | — |
| Oakdale Window Tint | Oakdale Window Tint | oakdaletint@gmail.com | (209) 390 3578 | Other | Oakdale · Stanislaus County | — | — |
| Octavio Sajuan Roofing | Sajuan Octavio | — | (209) 204 8000 | Other roofers | Keyes · Stanislaus County | — | — |
| Octavio Torres Barajas | Octavio Torres Barajas | — | (209) 568 9172 | Other | Ceres · Stanislaus County | — | — |
| Od Electric | Rany Oday Yonan | — | (209) 531 4237 | Electricians | Modesto · Stanislaus County | — | — |
| Odds N Ends Custom Concrete | Odds N Ends Custom Concrete | — | (209) 522 7334 | Other | Modesto · Stanislaus County | — | — |
| Ohana Pool Service LLC | Kaelin Walter Neese | ohanapool2017@gmail.com | (209) 620 0100 | Pool | Patterson · Stanislaus County | — | — |
| Olive Construction | Jose De Jesus Jasso Jimenez | — | (209) 678 0606 | GC, remodel, ADU | Newman · Stanislaus County | — | — |
| Oliveira & Son Construction INC | Frank Albert Oliveira | — | (209) 484 4041 | GC, remodel, ADU | Modesto · Stanislaus County | — | — |
| Oller Construction | David John Oller | — | (209) 604 4182 | GC, remodel, ADU | Modesto · Stanislaus County | — | — |
| Olp Contruction INC | Genaro Sr Infante Quiroz | — | (209) 303 9474 | GC, remodel, ADU | Modesto · Stanislaus County | — | — |
| Olvera Construction | Olvera Camacho Edgar | — | (209) 485 1589 | GC, remodel, ADU | Hughson · Stanislaus County | — | — |
| Omega Construction | Manula Pacheco Borges | — | (209) 648 3881 | GC, remodel, ADU | Turlock · Stanislaus County | — | — |
| On - Guard Systems INC | Rand Anthony Bartholomew | — | (209) 522 5240 | Electricians | Modesto · Stanislaus County | — | — |
| One In All Painter | One In All Painter | — | (209) 740 3116 | Windows, patio, painters | Modesto · Stanislaus County | — | — |
| One Roofing | Hameed Rahman Sohrabi | info@one-roofing.com | (510) 804 5700 | Other roofers | Modesto · Stanislaus County | — | — |
| Onesource Specialities | Adam Richard Noard | — | (209) 417 4335 | Other | Patterson · Stanislaus County | — | — |
| Ongrade Earthworks | Ongrade Earthworks | chad@ongradeearthworks.com | (209) 668 3258 | Other | Denair · Stanislaus County | — | — |
| Onkar Builders INC | Sukhbir Kaur Bhatti | — | (209) 538 2900 | GC, remodel, ADU | Modesto · Stanislaus County | — | — |
| Onr Construction | Victor Raul Ortega Quintero | info@onrconstruction.com | (209) 765 6794 | GC, remodel, ADU | Ceres · Stanislaus County | — | — |
| Ontrak Garage Doors | Ontrak Garage Doors | — | (209) 872 3694 | Other | Salida · Stanislaus County | — | — |
| Optimum Connections | Optimum Connections | — | (209) 675 4332 | Other | La Grange · Stanislaus County | — | — |
| Orbis Nexus INC | Oh Sangmin | — | (714) 616 1164 | Electricians | Turlock · Stanislaus County | — | — |
| Oro Development INC | Vanessa Orozco | — | (775) 835 3777 | GC, remodel, ADU | Turlock · Stanislaus County | — | — |
| Orozco's Floor Covering INC | De La Torre Osvaldo Orozco | — | (209) 409 0486 | Other | Ceres · Stanislaus County | — | — |
| Ortiz Custom Cabinets | Ortiz Custom Cabinets | — | (209) 272 9545 | Other | Modesto · Stanislaus County | — | — |
| Ortiz Lawn Care | Ortiz Lawn Care | — | (209) 581 8013 | Windows, patio, painters | Modesto · Stanislaus County | — | — |
| Oscorp Construction INC | Oscar Cervantes | — | (209) 765 2609 | GC, remodel, ADU | Modesto · Stanislaus County | — | — |
| Osvaldo Chavez | Osvaldo Chavez | — | (209) 681 4423 | GC, remodel, ADU | Modesto · Stanislaus County | — | — |
| Ouse Electrical Contracting | Marc Edward Ouse | — | (209) 535 0369 | Electricians | Turlock · Stanislaus County | — | — |
| Out-west Industries INC | Justin Dennis Hicks | — | (209) 604 6140 | Other | Oakdale · Stanislaus County | — | — |
| Outback Fencing INC | Errol Lindsay Frain | — | (530) 300 0298 | Other | Oakdale · Stanislaus County | — | — |
| Outdoor Living + | Gutierrez Alondra Martinez | — | (408) 396 0425 | Windows, patio, painters | Modesto · Stanislaus County | — | — |
| Overhaul Construction INC | Alvarez Francisco | — | (209) 243 9252 | Other roofers | Patterson · Stanislaus County | — | — |
| Overweg Plumbing | Overweg Plumbing | — | (209) 479 9434 | Other | Modesto · Stanislaus County | — | — |
| Oxytech | Keith Douglas Mattern | — | (209) 869 0205 | Other | Riverbank · Stanislaus County | — | — |
| Ozzie David Construction | Ozzie Koshaba David | — | (209) 410 2902 | GC, remodel, ADU | Ceres · Stanislaus County | — | — |
| P & F Metals | James Stephen Vieira | — | (209) 667 2515 | GC, remodel, ADU | Turlock · Stanislaus County | — | — |
| P & H Plumbing LLC | Philip Carrasco Jr Fuentes | — | (209) 408 3685 | Other | Modesto · Stanislaus County | — | — |
| P F C Quality Painting | P F C Quality Painting | sales@pfcqualitypainting.com | (209) 900 3758 | Windows, patio, painters | Ceres · Stanislaus County | — | — |