The Auburn Post Office is one of three separate buildings which share walls and an outside brick façade. This complex, built in 1855, is known as the James Block or Post Office Block. Another building in this complex was the Wells Fargo Express Co.

The Auburn Post Office is the oldest operating post office west of the Mississippi. Mail service began in Auburn in 1849. A post office was established in 1853 and moved to this building in the late 1870s.