Reserve is a census-designated place (CDP) in Sheridan County, Montana, United States.

[4] According to the United States Census Bureau, the CDP has a total area of 1.4 square miles (3.6 km2), all land.

There were 25 housing units at an average density of 18.2 per square mile (7.0/km2).

33.3% of all households were made up of individuals, and 11.1% had someone living alone who was 65 years of age or older.

There were 41.7% of families and 33.3% of the population living below the poverty line, including 40.0% of under eighteens and 66.7% of those over 64.