Willis Tower in Chicago

Willis Tower, formerly named Sears Tower, is a 108-story 1451-foot (442 m) in Chicago Illinois. At the time of its completion in 1974, it was the tallest building in the world, spasursing the Trade Center towers in New York, and it held this rank for nearly 25 years. The Willis Tower is the tallest building in the United States and the fifth-tallest freestanding structure in the world as well as the fifth tallest building in the world of the roof.Although Sears'naming rights expired in 2003, the building continued to be called Sears Tower for several years. In March 2009 London-based insurance broker Willis Group Holdings,Ltd. agreed to lease a portion of the building and obtained the building's naming rights.On July 16, 2009, the building was officially renamed Willis Tower.