Basin is an unincorporated community and census-designated place (CDP) in Jefferson County, Montana, United States. It lies approximately 10 miles (16 km) southeast of the Continental Divide in a high narrow canyon along Interstate 15 about halfway between Butte and Helena. Basin Creek flows roughly north to south through Basin and enters the Boulder River on the settlement's south side. As of the 2020 census, Basin had a population of 199.