The Yellowstone Main Post Office in Yellowstone National Park was built in Mammoth Hot Springs as part of a facilities improvement program by the United States Post Office Department. The post office in Yellowstone was nominated to the National Register of Historic Places as part of a thematic study comprising twelve Wyoming post offices built to standardized USPO plans in the early twentieth century. The Yellowstone facility is an understated classical structure with a low hipped roof and rounded dormers that uses a plan and a basic design vocabulary similar to that used in other post offices in the program.