San Francisco International Airport is an international airport in an unincorporated area of San Mateo County, south of Downtown San Francisco. It has flights to points throughout North America and is a major gateway to Europe, the Middle East, Asia, and Oceania. SFO is the largest airport in the San Francisco Bay Area and the second-busiest in California, after Los Angeles International Airport (LAX). In 2017, it was the seventh-busiest airport in the United States and the 24th-busiest in the world by passenger count. It is the fifth-largest hub for United Airlines, which operates out of Terminal 3 and the International Terminal. SFO functions as United's primary transpacific gateway. Additionally, SFO is a major maintenance hub for United Airlines and houses the SFO Museum that was created in 1980, the first museum in an international airport. It also serves as a hub for Alaska Airlines, which operates in Terminal 2. The airport is owned and operated by the City and County of San Francisco and lies in a ZIP code assigned to San Francisco. However, it is located outside of San Francisco in unincorporated San Mateo County. Between 1999 and 2004, the San Francisco Airport Commission operated city-owned SFO Enterprises, Inc., to oversee its business purchases and operations of ventures. History The City and County of San Francisco first leased at the present airport site on March 15, 1927, for what was then to be a temporary and experimental airport project. San Francisco held a dedication ceremony at the airfield, officially named the Mills Field Municipal Airport of San Francisco, on May 7, 1927, on the 150-acre cow pasture. The land was leased from the Mills Estate in an agreement made with Ogden L. Mills who oversaw the large tracts of property originally acquired by his grandfather, the banker Darius O. Mills. San Francisco purchased the property and the surrounding area expanding the site to beginning in August 1930. The airport's name was officially changed to San Francisco Airport in 1931 upon the purchase of the land. "International" was added at the end of World War II as overseas service rapidly expanded. Early operations The earliest scheduled carriers at the airport included Western Air Express, Maddux Air Lines, and Century Pacific Lines. United Airlines was formed in 1934 and quickly became the key carrier at the airport, with Douglas DC-3 service to Los Angeles and New York beginning in January