O Hare International Airport (IATA: ORD, ICAO: KORD, FAA LID: ORD), also known simply as O Hare Airport or O Hare, is a major airport located in the northwestern-most corner of Chicago, Illinois, United States, 17 miles (27 km) northwest of the Chicago Loop. It is the largest hub of United Airlines (whose headquarters are in downtown Chicago) and the second-largest hub of American Airlines (after Dallas-Fort Worth International Airport). It is operated by the City of Chicago Department of Aviation, associated with an umbrella regional authority.