Chicago O'Hare International Airport , also known as O'Hare Airport, Chicago International Airport, Chicago O'Hare or simply O'Hare, is an international airport located on the Far Northwest Side of Chicago, Illinois, United States, northwest of the Loop. It is the primary airport serving the Chicago area, with Midway Airport, about closer to the Loop, serving as a secondary airport. It is operated by the City of Chicago Department of Aviation. Most of O'Hare Airport is in Cook County, but a section of the southwest part of the airport is in DuPage County. The airport is located within a section of the City of Chicago contiguously connected to the rest of the city via a narrow strip of land about wide, running along Foster Avenue, from the Des Plaines River to the airport. This land was annexed into the city limits in the 1950s to assure the massive tax revenues associated with the airport would go to the city. The strip is bounded on the north by Rosemont and the south by Schiller Park.