<P> The Willis Tower , built as and still commonly referred to as the Sears Tower , is a 110 - story , 1,450 - foot ( 442.1 m ) skyscraper in Chicago , Illinois , United States . At completion in 1973 , it surpassed the World Trade Center towers in New York to become the tallest building in the world , a title it held for nearly 25 years and remained the tallest building in the Western Hemisphere until 2014 and the completion of a new building at the World Trade Center site . The building is considered a seminal achievement for its architect Fazlur Rahman Khan . The Willis Tower is the second - tallest building in the United States and the Western hemisphere -- and the 16th - tallest in the world . More than one million people visit its observation deck each year , making it one of Chicago 's most popular tourist destinations . The structure was renamed in 2009 by the Willis Group as part of its lease on a portion of the tower 's space . </P>
<P> The Willis Tower , built as and still commonly referred to as the Sears Tower , is a 110 - story , 1,450 - foot ( 442.1 m ) skyscraper in Chicago , Illinois , United States . At completion in 1973 , it surpassed the World Trade Center towers in New York to become the tallest building in the world , a title it held for nearly 25 years and remained the tallest building in the Western Hemisphere until 2014 and the completion of a new building at the World Trade Center site . The building is considered a seminal achievement for its architect Fazlur Rahman Khan . The Willis Tower is the second - tallest building in the United States and the Western hemisphere -- and the 16th - tallest in the world . More than one million people visit its observation deck each year , making it one of Chicago 's most popular tourist destinations . The structure was renamed in 2009 by the Willis Group as part of its lease on a portion of the tower 's space . </P>
when did the sears tower become the willis tower
when did the sears tower become the willis tower
in 2009
in 2009