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Official Name

Aon Center


200 E. Randolph St.

Completion Date




Chicago’s third-tallest building stands out in Chicago’s skyline, distinctively different from its steel-and-glass peers. Its history is rather more colorful than the stark white stone in which it is clad.

"Big Stan"

In the late 1960s, the Standard Oil Company of Indiana wanted a consolidated downtown Chicago headquarters. With a prominent site at the head of Grant Park (vacated by industry), their building needed to be monumental. The company hired Edward Durell Stone, whose unique brand of Modernism was then in vogue; his Kennedy Center would open in Washington, DC, in 1971. When the tower opened in 1973, it was the second-tallest building in Chicago and the world.


Architects of record Perkins + Will used a relatively new structural form for the tower. Elevators and other services are bundled together in the core, while the perimeter columns define an outer tube. The inner and outer tubes are linked by trusses that support the large open floor plates, and the entire arrangement provides the structure that keeps the building standing. A related tube-based structure was used in the Willis (Sears) Tower, under construction at the same time.


What's in a name?

Standard Oil became Amoco in 1985, and the building rebranded too. Another name-change arrived in 1998, when the building was sold and renamed Aon Center after one of its major tenants. Perhaps its several names have helped prevent the building from gaining quite the same iconic status as Chicago’s other tall buildings. Nonetheless, even as newer structures have sprouted nearby, Aon Center remains a timeless and elegant piece of Modernist architecture that graces Chicago’s skyline.

Beauty is more than skin-deep

The architect originally clad the building’s numerous columns in white Carrara marble, the same stone used by famous sculptors for centuries. The material was beautiful, but stood up poorly to the wild temperature swings of Chicago weather. Cracks eventually formed, and in the early 1990s the entire building was re-faced with much more durable granite—at tremendous cost.