Aon Center

The Aon Center (200 East Randolph Street, formerly Amoco Building) is a modern skyscraper in the Chicago Loop, Chicago, Illinois, United States, designed by architect firms Edward Durell Stone and The Perkins and Will partnership, and completed in 1973 as the Standard Oil Building. With 83 floors and a height of 1,136 feet (346 m), it is the third tallest building in Chicago, surpassed in height by the Willis Tower and the Trump International Hotel and Tower. The building is managed by Jones Lang LaSalle. Aon has the headquarters of the Aon Corporation, and it formerly had the headquarters of Amoco.


The Standard Oil Building was constructed as the new headquarters of the Standard Oil Company of Indiana, which had previously been housed at South Michigan Avenue and East 9th Street. When it was completed in 1973 it was the tallest building in Chicago and the fourth-tallest in the world, earning it the nickname "Big Stan". (A year later, the Sears Tower took the title as Chicago's and world's tallest.) The building employs a tubular steel-framed structural system with V-shaped perimeter columns to resist earthquakes, reduce sway, minimize column bending, and maximize column-free space. This construction method was also used for the World Trade Center towers in New York City.

When completed, it was the world's tallest marble-clad building, being sheathed entirely with 43,000 slabs of Italian Carrara marble. The marble used was thinner than previously attempted in cladding a building; this quickly proved to be a mistake. In 1974, just a year after completion, one of the marble slabs detached from the façade and penetrated the roof of the nearby Prudential Center. Further inspection found numerous cracks and bowing in the marble cladding of the building. To alleviate the problem, stainless steel straps were added to hold the marble in place. Later, from 1990 to 1992, the entire building was refaced with Mount Airy white granite at an estimated cost of over $80 million. (Amoco was reluctant to divulge the actual amount, but it was well over half the original price of the building, without adjustment for inflation.) Two-thirds of the discarded marble was crushed and used as landscaping decoration at Amoco's refinery in Whiting, Indiana, one-sixth was donated to Governor's State University, in University Park, Illinois, and one-sixth donated to Regalo, a division of Lashcon Inc. Under a grant from the Illinois Department of Rehabilitative Services, Regalo's 25 handicapped workers carved the discarded marble into a variety of specialty items such as corporate gifts and mementos including desk clocks and pen holders. The building's facade now somewhat resembles that of the former World Trade Center due to the upward flow of the columns.

The Standard Oil Building was renamed the Amoco Building when the company changed names in 1985. In 1998, Amoco sold the building to The Blackstone Group for an undisclosed amount, estimated to be between $430 and $440 million. It was renamed as the Aon Center on December 30, 1999, although the Aon Corporation would not become the building's primary tenant until September 2001. In May 2003, Wells Real Estate Investment Trust, Inc. acquired the building for between $465 and $475 million. (On August 10, 2007, Wells Real Estate Investment Trust, Inc. changed its name to Piedmont Office Realty Trust, Inc.)

Exterior lighting

In recent years, the top floors of the building have been lit at night with colors to reflect a particular season or holiday. Orange is used for Thanksgiving, green or red for Christmas, and pink during Breast Cancer Awareness Month. The lighting commonly matches the nighttime lighting on the antenna of Willis Tower, the John Hancock Center and the upper floors of the Merchandise Mart.


In the plaza, there is a sounding sculpture by Harry Bertoia.


  • Aon Corporation maintains its headquarters in the Aon Center.
  • Chicagoland Chamber of Commerce, Suite 2200
  • BP (formerly British Petroleum), successor to Amoco and Standard Oil of Ohio
  • Jones Lang LaSalle
  • Daniel Edelman Inc.
  • Marketing Support Inc.
  • ThoughtWorks
  • R.H. Donnelley
  • Strata Decision Technology
  • The Mid-America Club
  • Veolia
  • Microsoft

Position in Chicago's skyline


5 photos

Building Activity

  • OpenBuildings
    OpenBuildings updated 17 media and removed a media
    about 4 years ago via
  • Teodora Todorova
    Teodora Todorova updated 15 media and uploaded 3 media
    bohi aon and blue cross blue shield xswh 20060607 840x1500 chicago aon building zjzo aon center
    about 5 years ago via
  • updated a digital reference
    about 5 years ago via Annotator