U.S Assay office building – Boise
Excellence in Historic Preservation

The U.S. Assay Office in downtown Boise, one of only three National Historic Landmark buildings in Idaho, has been carefully and comprehensively restored, earning it a 2025 Orchid Award for Excellence in Historic Preservation. Originally built in 1871 to serve Idaho’s booming gold and silver mining industry, the Assay Office played a vital role in connecting the Idaho Territory to the federal treasury. Designed by renowned architect Alfred B. Mullett and constructed from locally quarried sandstone, the building is a rare and significant example of Italian Villa–style architecture in the region.

The recent restoration, led by CSHQA and the Idaho State Historical Society, prioritized preserving original materials, repairing damaged sandstone, restoring historic plaster, refinishing wood floors, and updating mechanical systems with sensitivity to the building’s legacy. Funded through a combination of state and federal grants, including Save America’s Treasures, the project also included landscape enhancements funded by St. Luke’s, interpretive signage, and archaeological discoveries from the building’s mining past.

Now home to the Idaho State Historic Preservation Office, the Assay Office continues to educate and inspire, standing as a lasting symbol of Idaho’s early mining economy and its enduring architectural heritage.

Project Acknowledgements:

Photos: CSHQA and after images by © Tobin Rogers Photography