The Treasury Department has been located next to the White House since the federal government moved to Washington, D.C. from Philadelphia in 1800. The building and the Department have been a part of the history of the nation through times of triumph and crisis. During the American Civil War the building was under construction and served as a fortification in the capital against any potential Confederate attack. The nation's finances were also protected and managed to help fund the war effort.

The Treasury and the U.S. Capitol buildings were the only major federal buildings in Washington, D.C. whose construction continued during the years of the Civil War (1861-1865). Building materials, manpower and financial resources were all in short supply as the war consumed the attention of the nation. While challenging, the work on the South Wing of the Treasury building neared completion just as the war began. Some of the first offices originally meant for Treasury staff were occupied by military commanders of the Union forces. As troops poured into the city, a regiment from Massachusetts set-up camp in the courtyard of the Treasury building.

Initially, it was hoped the Civil War would be short in duration, but as the war went on the cost of supporting the war effort was draining the finances of the nation. Serving in office throughout the Civil War, Secretary Chase was able to initiate major changes in the U.S. economy, establishing a national banking system and issuing the first federal currency, the so called "greenback" paper money.