Mill Valley is a city in Marin County, California, United States, located about 14 miles (23 km) north of San Francisco via the Golden Gate Bridge. The population was 13,903 at the 2010 census.

Mill Valley is located on the western and northern shores of Richardson Bay, and the eastern slopes of Mount Tamalpais. Beyond the flat coastal area and marshlands, it occupies narrow wooded canyons, mostly of second-growth redwoods, on the southeastern slopes of Mount Tamalpais. The Mill Valley 94941 ZIP code also includes the following adjacent unincorporated communities: Almonte, Alto, Homestead Valley, Tamalpais Valley, and Strawberry. The Muir Woods National Monument is also located just outside the city limits.