Atlanta, Georgia, has the busiest airport in the United States, no matter how you measure it, either by number of passengers getting on or off a plane, or by the number of takeoffs and landings.
Passengers who are just passing through don’t count
Chicago’s O’Hare International Airport comes in second, followed by the Los Angeles and Dallas–Fort Worth airports.
Those four U.S. airports are also the world’s busiest airports.
By number of passengers, they are followed by London (Heathrow), Tokyo, Frankfurt, and Paris (Charles de Gaulle).