Manderson is located at 44°16'9" North, 107°57'47" West (44.269167, -107.963056).
According to the United States Census Bureau, the town has a total area of 0.90 mi2 (2.34 km2). 0.84 mi2 (2.18 km2) of it is land and 0.06 mi2 (0.16 km2) of it is covered by water. The total area is 6.90% water.
Manderson is located in the Mountain Standard Time (MST) timezone, GMT-07:00. It observes Daylight Saving Time (DST).