San Francisco is in California.
San Francisco ( initials SF ) ( [ sæn_frənˈsɪskoʊ ] , Spanish for Saint Francis ; Spanish : [ san franˈsisko ] ) , officially the City and County of San Francisco , is the cultural , commercial , and financial center of Northern California . Located at the north end of the San Francisco Peninsula , San Francisco is about 47.9 sqmi in area , making it the smallest county -- and the only consolidated city-county -- within the state of California . With a density of about 18,581 people per square mile ( 7,174 people per km2 ) , San Francisco is the most densely settled large city ( population greater than 200,000 ) in California and the second-most densely populated major city in the United States after New York City . The San Francisco Bay Area ( referred to locally as the Bay Area ) is a populous region surrounding the San Francisco and San Pablo estuaries in Northern California .