Prairie County is a county in the U.S. state of Montana. As of the 2020 census, the population was 1,088, making it the fifth-least populous county in Montana. Its county seat is Terry. Prairie County was created by the Montana Legislature in 1915 out of parts of Custer, Dawson, and Fallon Counties. The name was selected in a contest and reflects the predominant landscape of the region.

Terry, incorporated in 1910, is a town and the county seat of Prairie County, Montana, United States. The population was 562 at the 2020 census.