Due to the difficulty of transporting ores, which can be heavy, the long distance to the nearest U.S. Mint in San Francisco, there was great demand for an assaying office in Idaho[3] that would be able to separate precious metals from impurities in them, helping to place a value on ores that went through the office.

The city block site bounded by Main, First, Idaho and Second was donated by Alexander Rossi, a prominent citizen of Boise.

The building featured a cupola for ventilation and the interior doors were equipped with iron cages.

This slump lasted about a decade until further gold strikes were made in the northern part of the state.

[3] Renovations on the building in 1889 and 1890 included a new fence, new floors, a hot and cold water system and electric lights.

The Assay Office was declared a National Historic Landmark in 1961, recognizing its significant role in the state's development.