"United and Chicago are inextricably linked, and this move further deepens our commitment to the city and region," Glenn Tilton, United chairman and CEO, said in a release. "Willis Tower is a world-class building that offers a much-improved working environment for our people and the flexibility to adapt to the many changes that are inherent in our industry."

The decision to relocate to Chicago came after several months of examining potential sites both in the city and the suburbs. The move will also put AUL closer to United's Operations Center at 77 W. Wacker Dr.

The 2,800 employees will begin moving from the Elk Grove location during the fall of 2010. Only two-thirds of the current location are currently being utilized.

"We believe that Chicago is the ideal place to run a business, because our city offers tremendous economic strength and resources combined with an enhanced quality of life," Mayor Richard M. Daley, said in a release. "During this tough economy, United's move is a show of confidence in Chicago and our economic future. This is a positive moment for our city."