Willis Tower Fast Facts - CNN.com (CNN) -- Here's some background information about the Willis Tower, located in Chicago. The second tallest skyscraper in the North America, Willis Tower stands at 110 stories and 1,730 feet (the tallest is One World Trade Center at 1,776 feet). Formerly the Sears Tower, it is now named for its tenants, Willis Group Holdings. The visitors' observation deck, called the "Skydesk," is located on the 103rd floor. Other Info: With clear weather, four states are viewable up to 50 miles away: Michigan, Indiana, Illinois, Wisconsin. Sears Tower was the world's tallest building until 1996, when it was surpassed by the Petronas Twin Towers. 25,000 people enter the skyscraper every day. 1.3 million visitors go up to the Skydeck each year. The Skydeck elevator can travel to the Skydeck in one minute, ten seconds. Characteristics: Structural Height - 1,450 feet or 110 floors Height with the two antennas - 1,730 feet Height to Skydeck/103rd floor - 1,353 feet Lowest level - 43 feet below Franklin St. Building Size - 4.5 million gross square feet Weight - 222,500 tons or 445 million pounds Cost to build - $150 million Windows - 16,100 Building exterior - black aluminum and bronze-tinted glass Architectural firm - Skidmore, Owings & Merrill Architect - Bruce Graham Structural Engineer - Fazlur Khan Timeline: 1970 - Construction begins May 3, 1973 - Construction is completed, the last floors are "topped out." 1973 - The Sears Tower is open to tenants 1974 -- The Skydeck opens to the public 1994 -- Sears, Roebuck and Co. sells the building to Aldrich, Eastman & Waltch December 3, 1997 -- AEW Partners LP sells the building to Canadian real estate firm, TrizecHahn Corp. 1998 - The Petronas Twin Towers in Kuala Lumpur, Malaysia surpass the Sears Tower in height to become the world's tallest buildings at 1,483 feet each. The Sears Tower is now the world's second tallest building. August 28, 2003 - MIAC (Metropolitan Insurance and Annuity Company), an affiliate of MetLife, purchases the tower. March 2009 - The owners of the Sears Tower announce that the building will be renamed the Willis Tower in 2009, after new tenant Willis Group Holdings. July 2009 - Skydeck's attraction, the Ledge, opens on the 103rd floor. It is a series of glass bays, with glass floors, that extend 4.3 feet outwards from the building. Visitors can now look directly down 1,353 feet to the street below. August 2009 - The Sears Tower is officially renamed the Willis Tower. January 2010 - The Burj Khalifa in Dubai, U.A.E., becomes the world's tallest building measured at 2,717 feet, making the Willis Tower the world's fourth tallest building.