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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.
1 A bold form was chosen for the Hancock Center. 2  The original plan called for two buildings to be built on the site. 3  The building includes a mix of residential apartments, a parking garage, and retail and office space, with lounging, dining, and observatory facilities on the 94th, 95th, and 96th floors.