One South Dearborn is a 571 ft (174m) tall skyscraper in Chicago, Illinois. It was constructed from 2003 to 2005 and has 39 floors. DeStefano Keating Partners designed the building, which is the 71st tallest in Chicago as of November 2022. An earlier proposal for the same site proposed a much taller 112-story building. The current anchor tenant is Sidley Austin LLP, which moved into One South Dearborn in November 2005 from Bank One Plaza.