South Amherst is a census-designated place (CDP) in the town of Amherst in Hampshire County, Massachusetts, United States. The population was 5,039 at the 2000 census. There are two centers of development in South Amherst: Amherst Woods (a community of expensive single-family mostly owner-occupied homes) and the Mill Valley apartment complexes (The Brook, The Boulders, Mill Valley, Southpoint; mostly rental apartments). These two communities have, respectively, the most and least expensive housing in Amherst.