O'Hare began as Orchard Place, a site northwest of Chicago where Douglas built C-54 transports during the Second World War. The city acquired the field after the war as a successor to cramped Midway. In 1949 it was renamed for Lieutenant Commander Edward "Butch" O'Hare, a Chicago-born Navy ace awarded the Medal of Honor.
The airport code ORD still preserves the old Orchard name. Commercial airlines shifted over from Midway in the late 1950s as the jet age demanded longer runways. By the early 1960s O'Hare had seized the title of the world's busiest airport, a crown it held for most of the next three decades.
United and American both built enormous hubs at O'Hare. The airport pioneered ideas from dual parallel taxiways to the futuristic United Terminal 1 by Helmut Jahn, opened in 1987 with its neon-lit underground walkway. The International Terminal 5 followed in 1993. Chronic delays from crossing runways led to the O'Hare Modernization Program, which between 2005 and 2021 rebuilt the airfield into six parallel east-west runways plus two diagonals. The next act, O'Hare 21, includes satellite concourses and a new Global Terminal replacing Terminal 2.