The Commissioner's office was the first stone building erected at Fort Yellowstone and included an office, jail, and residential space on the first floor and bedrooms upstairs. The one-and-a-half-Story, rock-faced ashlar sandstone building stands by itself near the Hot Springs terraces. The building has a rectangular plan and a stone foundation. The gable-on-hip roof is covered with wood shingles and features two interior stone chimneys. The majority of the windows are one-over-one-light double-hung sash.
The front (northeast) features a full-width open porch with a hipped roof supported by six square posts that is accessed via a set of wood stairs. The entrance, which has a paneled and glazed door, is centered inside the porch and flanked by two windows. There are two front shed roof wall dormers, each with a single window. The southeast wall has an off-center entrance flanked by windows and two shed roof dormers. The rear (southwest) has an off-center entrance, three small windows that correspond to the location of the jail cells, and two through-the-cornice shed roof dormers. The northwest wall has two windows on the first story and two shed roof dormers.