On May 17, 1870, Companies B and C of the 17th U.S. Infantry, under command of Captain Edward P. Pearson, officially established the "Post at Cheyenne River Agency.

Andrew S. Bennett of the 5th Infantry who was killed September 4, 1878, near Clark's Fork, Montana Territory, in a battle with the Bannock Indians.

In 1891, the Great Sioux Reservation having been reduced and divided, after the ratification, of the treaty of 1889, the fort was abandoned and the Cheyenne River Agency was moved fifty-six miles up the Missouri River, opposite Forest City, Potter County, South Dakota, where administered the affairs of these Indians.

As a result of the construction of Oahe Dam, the agency was later moved to Eagle Butte, South Dakota.

The disposition of the Indians at the agency who receive rations all the year round, or nearly so, is good, with the exception of the young men, who are not reliable.