Aon Center

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The Aon Center is a skyscraper at 200 East Randolph Street, in the northeast corner of the Chicago Loop in Illinois, USA. It has 83 floors and stands 346 metres (1,136 feet) tall. When it was finished in 1973 it was called the Standard Oil Building, and people nicknamed it "Big Stan."

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At a glance

Country: United States
Location: Chicago, USA
Built: 1973
Height: 346 m
Type: Skyscraper

Quick answers

Where is Aon Center?

Aon Center is in Chicago, USA, United States.

When was Aon Center built?

Aon Center was built in 1973.

How tall is Aon Center?

Aon Center is about 346 m tall.

A plain square shaft ribbed with white chevron-shaped piers, one of Chicago's tallest.

It was designed by a partnership of the firms Edward Durell Stone and Perkins and Will. Today it is the fourth-tallest building in Chicago, but at the time it opened it was the fourth-tallest building in the whole world, behind only the twin towers of the original World Trade Center and the Empire State Building.

How was it built?

The tower uses a tube-shaped steel frame. Its outer walls are lined with V-shaped columns, which help the building resist earthquakes, sway less in the wind, and leave the floors inside open and free of columns. The original World Trade Center twin towers in New York used the same building method. Older skyscrapers often hid their strength in heavy columns inside; here the strength sits in the outer wall.

Marble, then granite

When the tower was new, it was covered in white marble, which made it the tallest marble-clad building in the world. The marble was later replaced with granite. For a short time it was Chicago's tallest completed building, until the Sears Tower (now Willis Tower) passed it in 1974. The building is managed by JLL, which also has its own headquarters inside.

Fun facts

It was first clad in Italian Carrara marble, later replaced with granite.
It was first covered in Italian Carrara marble, which was later swapped for granite.
Its nickname "Big Stan" comes from its first owner, the Standard Oil Company of Indiana.
Today it is home to the headquarters of Aon, the Blue Cross Blue Shield Association and Kraft Heinz.