San Francisco, officially the City and County of San Francisco, is a commercial, financial, and cultural center of Northern California. With a population of 827,526 residents as of 2024, San Francisco is the fourth-most populous city in the U.S. state of California and the 17th-most populous in the United States. San Francisco has a land area of 46.9 square miles (121 square kilometers) at the upper end of the San Francisco Peninsula and is the fifth-most densely populated U.S. county. Among U.S. cities proper with over 250,000 residents, San Francisco is ranked first by per capita income and sixth by aggregate income as of 2023. San Francisco anchors the 13th-most populous metropolitan statistical area in the U.S., with almost 4.6 million residents in 2023. The larger San Jose–San Francisco–Oakland combined statistical area, the fifth-largest urban region in the U.S., had a 2023 estimated population of over nine million.

Prior to European settlement, the modern city proper was inhabited by the Yelamu. On June 29, 1776, settlers from New Spain established the Presidio of San Francisco at the Golden Gate, and the Mission San Francisco de Asís a few miles away, both named for Francis of Assisi. The California gold rush of 1849 brought rapid growth, making it the largest city on the West Coast at the time. In 1856, San Francisco became a consolidated city-county.