San Mateo is a city in San Mateo County, California, United States, on the San Francisco Peninsula. About 20 miles south of San Francisco, the city borders Burlingame to the north, Hillsborough to the west, San Francisco Bay and Foster City to the east and Belmont to the south. The population was 105,661 at the 2020 census. San Mateo has a Mediterranean climate and is known for its rich history at the center of the San Francisco Bay Area.