As the name implies, the guardhouse is the building that housed the guard detail. The guard detail was chosen from among the men in what was sometimes a fierce competition. While guard duty meant walking sentry duty, it also meant exemption from other fatigue details. Soldiers competing for guard detail were judged on the appearance of their dress uniform and mastery of drill.

In addition to housing the guard, the guardhouse also served as a prison. There were 4 different prison rooms. The garrison prison room was a minimum security room used for members of the post garrison being confined for minor rule infractions. The general prison room was for civilian prisoners or deserters from other posts, being detained at Fort Hartsuff. The dark cell room was for a member of the post garrison who committed more serious infractions such as drunk and disorderly or gambling. The dark cells were small wood boxes where you could not stand up or move around much. In the winter you would get a blanket and a slop jar. In the summer you just got a slop jar. There was a 14 ft x 23 ft exercise pen with a latrine in the corner on the back of the building. The prisoners were allowed to exercise about a half-hour in the morning and evening and to empty their slop jars. The Commanding Officer determined their length of sentence. The ordnance storeroom held all rifles, ammunition, and related items when they were not being used by troops in the field. Sometimes the troops at Fort Hartsuff helped local law enforcement catch outlaws. One such event happened on July 27, 1879, when a detachment of soldiers led by Captain Munson helped some U.P. Railroad detectives capture Doc Middleton, a local horse thief.

Domeier, Jim . "The Guide to Fort Hartsuff (1874-1881)." . .