Basin is a census-designated place (CDP) in Jefferson County, Montana. It is part of the Helena Micropolitan Statistical Area, and its population at the 2000 census was 255.
Evidence of human habitation from 10,000 years ago has been found at a site near Clancy, 20 miles (32 km) from Basin. The CDP is situated above the Boulder Batholith, the host rock for many valuable mineral ores found in this part of the state. Gold and silver mining became popular, but gradually the ores got depleted and mining activity declined. Evidence of the mining activity has persisted into this century.
Till 2011 Basin had the Montana Artists Refuge. Small-scale mining, reworking of old mine dumps, and placer mining has continued in the region, after the initial boom faded.
The population predominantly comprises White Americans. A small percentage of the population comprises Native Americans and people of Hispanic origin.