Greenbrae is a small unincorporated community in Marin County, California, United States. It is located 1.5 miles (2 km) south-southeast of downtown San Rafael, at an elevation of 33 feet, and 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 Kentfield. The community is served by area codes 415 and 628