Greenbrae is a small unincorporated community  in Marin County, California. It is located south-southeast of downtown San Rafael, at an elevation of 33 feet (10 m), located adjacent to U.S. Route 101 at the opening of the Ross Valley. Part of Greenbrae is an unincorporated community of the county while the remaining area is inside the city limits of Larkspur. The ZIP code is 94904, and is shared with the neighboring Census-designated place (CDP) of Kentfield. The community is in area codes 415 and 628.