O'HARE's Airport Code is ORD, which stands for Chicago O'HARE International Airport. Located in Chicago, Illinois, it is the third busiest airport in the world and the second busiest in the United States. It is a major hub for American Airlines and United Airlines, and serves as a focus city for Frontier Airlines. ORD is the primary airport serving the Chicago metropolitan area and is a major gateway to destinations across the United States, Canada, Mexico, the Caribbean, and Europe.