CHICAGO – United Airlines is moving its corporate headquarters into the nation's tallest building.

Willis Tower is already home to United's Network Operations Center. Once the airline's corporate headquarters moves across Chicago's Loop into Willis, officials say United will occupy approximately 25 percent of the 110-story building. The new deal means United will be leasing a total of 830,000 square feet at Willis, occupying 16 floors.

In announcing the deal Monday, Chicago Mayor Rahm Emanuel said United's decision to extend its commitment to the city's downtown is "great news for all Chicagoans."