The Illinois expansion will happen at the company’s headquarters campus in Abbott Park. It's also growing in Dallas.

Landmark opened in 1973 with original tenant Sears Roebuck & Co. CHICAGO, Illinois (CNN) -- Sears Tower is history. As of Thursday, the iconic Chicago, Illinois, skyscraper is now named Willis Tower.

An curved arrow pointing right. The Ledge is a glass box on the 103rd floor of the Willis Tower, the eighth-tallest building in the world and the tallest building in the Western hemisphere.

Chicago is home to one of the tallest buildings in the world: the Willis Tower. So tall that on a windy day, the topmost floors can sway as much as three feet. But what keeps it from falling?

Willis Tower and its Skydeck sit above South Wacker Drive on the western edge of the Loop. You'll find the Quincy/Wells L station nearby, as well as several bus stops and a parking garage.

Chicago is home to one of the tallest buildings in the world: the Willis Tower. So tall that on a windy day, the topmost floors can sway as much as three feet. But what keeps it from falling?