Muir Beach is a census designated place (CDP), unincorporated community, and beach on the Pacific Ocean. The community is located 16.5 miles (26.6 km) northwest of San Francisco in western Marin County, California, United States. Unlike many other entities in the area, it is not named directly in honor of conservationist John Muir; instead, it was named after Muir Woods National Monument to capitalize on the latter's popularity. The population was 304 at the 2020 census. The community itself flanks the northwest side of the beach.

Muir Woods National Monument is a United States National Monument managed by the National Park Service and named after naturalist John Muir. It is located on Mount Tamalpais near the Pacific coast in southwestern Marin County, California. The Monument is part of the Golden Gate National Recreation Area, and is 12 miles (19 km) north of San Francisco. It protects 554 acres (224 ha), of which 240 acres (97 ha) are old growth coast redwood forests, one of a few such stands remaining in the San Francisco Bay Area.