San Francisco officially the City and County of San Francisco, is a cultural, commercial, and financial center in the U.S. state of California. Located in Northern California, San Francisco is the 17th most populous city proper in the United States, and the fourth most populous in California, with 873,965 residents as of 2020.[15] It covers an area of about 46.9 square miles (121 square kilometers),[20] mostly at the north end of the San Francisco Peninsula in the San Francisco Bay Area, making it the second most densely populated large U.S. city, and the fifth most densely populated U.S. county, behind only four of the five New York City boroughs.