(Brevet Lt. Col.) William G. Rankin, first established a camp on the site on June 15, 1866, with orders to build a post, the majority of which was built using adobe and cottonwood enclosed by a wooden stockade.

The second night after arrival the camp was attacked by a band of the Hunkpapa Lakota led by Sitting Bull, they were driven off with one soldier wounded.

The next day, the same group attacked and attempted to drive off the company's herd of beef cattle, but were repulsed and two Lakota killed.

Parties of men cutting and rafting logs from the mouth of the Yellowstone were often attacked and driven to camp, where the fighting often lasted from two to six hours with losses on both sides.

Hiram H. Ketchum with sixty men reacted, drove off the Indians and recovered the bodies with slight loss to his detachment.

The siege cut off the garrison from the nearby Missouri River and forced them to sink shallow wells near their quarters in order to obtain fresh water.

The episode began when the Philadelphia Inquirer ran a story April 1, 1867, based on a letter allegedly written from the fort, which was then picked up and run the next day nationwide.

Although by April 4 many newspapers had begun to question the validity of the report, The Chicago Daily Times, Detroit Free Press, New York Daily Tribune, The New York Times, and Boston Herald, among others, continued to feed the rumors with further stories for another month, many of them accusing the Army and the Johnson Administration of covering up the massacre.

The post was expanded again in 1871–1872 with the arrival of Colonel William B. Hazen's 6th Infantry Regiment to a six-company infantry post covering approximately a square mile, including laundress' quarters and other civilian areas, using lumber shipped from the Eastern United States by steamboat but with no stockade.

Beyond this double row the stone Powder Magazine was built in 1875 out of sandstone quarried from an area located to the North of the fort.

At the peak of occupation, which followed the Battle of the Little Bighorn in 1876 until 1881, there were just under 100 buildings and approximately 1,000 people occupying the post at any given moment including infantry and cavalry companies bivouacking in tents on the parade ground while being resupplied.

At the same time, the kitchen and mess hall for each barracks was relocated from the main building to a new addition connected by a short hallway.

From 150 to 200 migrants, led by Bobtail Bull and Crow Flies High, founded a new settlement of mainly log cabins some two miles northwest of the fort.

[3]: 105  [4]: 106  The very grounds for the separatists to settle this close to the military fort "was the greater protection from the Sioux" it offered to a small village.

In the 1990s the former Officer of the Guard/Officer of the Day building was found being used as a pump house for the nearby irrigation canal and was relocated to its original location.