Plains is a town in Sanders County, Montana, United States. The population was 1,126 at the 2000 census. It was originally founded as Horse Plains. The name was later shortened to Plains when the US Postal Service established a presence in 1905.
Plains is located at 47°27′31″N 114°53′6″W / 47.45861°N 114.885°W / 47.45861; -114.885 (47.458504, -114.885024). The town straddles the Clark Fork River with the fairgrounds on one shore and the town proper on the other.
According to the United States Census Bureau, the town has a total area of 0.6 square miles (1.5 km²), all of it land.