Big Sandy is a town in Chouteau County, Montana, United States. The population was 605 at the 2020 census.

Chouteau County is a county located in the North-Central region of the U.S. state of Montana. As of the 2020 census, the population was 5,895. Its county seat is Fort Benton. The county was established in 1865 as one of the original nine counties of Montana, and named in 1882 after Pierre Chouteau Jr., a fur trader who established a trading post that became Fort Benton, which was once an important port on the Missouri River.