High Quality Content by WIKIPEDIA articles! Basin is a census-designated place (CDP) in Jefferson County, Montana, United States. It lies about 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. The population was 255 at the 2000 census.