Located at 2201 "C" Street NW, Washington, DC, 20520, the Harry S Truman Building is the third largest federal building in the Washington D.C. metropolitan area. The Pentagon and the Ronald Reagan Building occupy first and second place, respectively.

In September, 2000, the headquarters of the State Department was officially named the Harry S Truman Building. Previously, the building was unofficially called the Main State Building. It was constructed during the 1930s with the intention that it would house the Department of War. However, the Department of War never occupied the building since, by the time construction was complete, the military had already outgrown the building. Instead, the structure was used for the Department of State.

A large addition was completed in the early 1960s, after which the original building was informally called "Old State" with the addition identified as "New State."

More than 8,000 employees work in the Harry S Truman Building. The structure contains over 1.5 million usable square feet of space, corridors take up over 267,000 square feet and the roof area is about 7 acres. There are 43 elevators, over 4000 windows and about 34,000 fluorescent light fixtures that provide interior illumination.