In December of 1869, Congress appointed a commission to select a site and prepare plans and cost estimates for a new State Department Building. The commission was also to consider possible arrangements for the War and Navy Departments. To the horror of some who expected a Greek Revival twin of the Treasury Building to be erected on the other side of the White House, the elaborate Second Empire design of Alfred Mullett was selected, and construction of a building to house all three departments began in June of 1871.

Construction took 17 years as the building slowly rose wing by wing. When the OEOB was finished in 1888, it was the largest office building in Washington, with 4 1/2" granite walls, 16' ceilings, and nearly 2 miles of black and white marble tile corridors. Almost all of the interior detail is of cast iron or plaster; the use of wood was minimilized to insure fire safety. Monumental curving staircases of granite with over 4,000 individually cast bronze balusters are capped by four skylight domes and two stained glass rotundas.