The third military Fort Walla Walla was built adjoining ‘Steptoeville,’ a community that had grown up around the second fort. The new fort was more extensive and included an approximately square section military reservation. Along with officers’ quarters and troop barracks, it included stables, blacksmith's shop, granary, and a saw mill. Fifteen of the original structures (built 1857-1906) remain. Through its history, the post was home to dragoon, infantry, and cavalry companies, including the famous ‘Buffalo Soldiers’ from 1902-1904.
The post was involved in a number of actions, including the Battle of Steptoe Butte and the Wright Expedition in 1858, and two decades later during the Nez Perce War and Bannock-Paiute War. Except for a small contingent, Fort soldiers were recalled to the East at the outset of the Civil War. During those years the remaining troops were augmented by Oregon, Washington, and California militia companies. Congress attempted to abandon the post in 1865. The legislation stated the post was in Oregon, but since 1853 the post was actually in Washington Territory, precluding the action. The fort remained active until its official abandonment in 1910. It had a brief revival during World War I, before being turned over to the Veterans Bureau.