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Timeline. 1  1965: Plans for the John Hancock Center are announced. 2  1969: Construction is completed. 3  1972: The Hancock Center is surpassed by the Standard Oil Building (now the Aon Center) as the tallest building in Chicago.  1973: The residential portion of this building converts from apartments to condominiums.
The original structure was built in 1903 as the carriage house for the Alfred C. Harrison residence, for which he commissioned Philadelphia's then-most prestigious architectural firm, Cope & Stewardson, to design the house along with his residence and the Alfred C. Harrison building.