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Originally known as the Sears Tower, the Willis Tower is a 110-story, 1,454-foot skyscraper located in Chicago, Illinois. Completed in 1974, it held the title of the tallest building in the world for nearly 25 years until it was surpassed by the Petronas Towers in Kuala Lumpur, Malaysia in 1998. The building's name was changed to Willis Tower in 2009 after the Willis Group Holdings acquired naming rights.