By 1869, Congress had appropriated $300,000 to acquire a new site at Fifth and Mission Streets and construct a building. Plans were drawn under the supervision of Alfred B. Mullet, Supervising Architect of the Treasury Department from 1866 to 1874. Mullett’s design was Classical Greek Revival, Doric columns and Roman scale and proportions. Sandstone from Newcastle Island in British Columbia was shipped in by three schooners for the facing of the upper floors and for the six colossal columns on the portico. The basement walls were of Rocklin granite. On May 26, 1870, the cornerstone of the Mint was laid. The building opened on a rainy Saturday, November 5, 1874.
Mullett knew well that the Pacific Coast was subject to earthquakes, and with remarkable foresight he designed the Old Mint to "float" on its foundations in an earthquake, rather than shatter. His vision was validated when the mint rode out the severe earthquake of Wednesday, April 18, 1906, practically undamaged. Heroic efforts by Treasury Department employees, using only a one-inch hose connected to wells that had fortunately been built just weeks earlier, saved the mint, and $200 million in gold in its vaults, from the fire that destroyed commercial San Francisco after the earthquake. With the downtown area and its banks destroyed, the San Francisco Mint was the only financial institution able to open for business in San Francisco and it became the depository and treasury for the city's relief fund.
By 1934, one third of the United States' gold reserve was stored in the vaults of the San Francisco Mint.
After minting operations were transferred to the new San Francisco Mint on Duboce Avenue in 1937, the Treasury Department and other government agencies occupied the building. In 1961 the "Old Mint" as it became known locally, was designated a National Historic Landmark.
In January 2003, The San Francisco Museum and Historical Society’s plan to renovate the building and establish a permanent home for the San Francisco Museum won unanimous support from the Mayor’s Old Mint Task Force. On January 29th the Old Mint Task Force unanimously recommended that the City enter into exclusive negotiations with the Society for a 66-year lease. In June, the Board of Supervisors voted unanimously to allow the city to take possession of the vacant property from the federal government and to enter into exclusive negotiations with the Society to turn the building into a city museum.