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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 John Hancock Center was completed in 1970, and its gently sloping black steel form remains one of the most-recognizable structures in Chicagoâs famed skyline. A bold form was chosen for the Hancock Center.