Aon Center

The Aon Center is a 346-meter office skyscraper at 200 East Randolph Street in Chicago's Loop district, completed in 1973 in the International Modern style. Originally opened as the Standard Oil Building and later renamed for the Aon Corporation, it briefly held the title of Chicago's tallest building before the Sears Tower surpassed it. Its original white marble cladding had to be entirely replaced with granite in the 1990s after panels repeatedly detached — a structural failure that became a widely cited case study in facade engineering. The building is a corporate office tower with no public access or visitor facilities. The listed city of Evanston appears to be a metadata error; the building is located in downtown Chicago.