It is the southernmost neighborhood of Plymouth, and includes the section of town south of Massachusetts Route 25, at the border with Wareham and Bourne.
Buttermilk Bay is a non-census designated area of the town of Plymouth.
Buttermilk Bay is the most inland inlet of Buzzards Bay MA, and contains the villages of Indian Heights, Indian Mound Beach, Hideaway Village, and others.
It's outlet into Buzzards Bay -- known to locals as "The Channel" is a narrow waterway bridged by Route 28, eventually continuing into the Cape Cod Canal.
In the past, due to the overflowing student enrollments of the 14 elementary schools in Plymouth, students who reside in Buttermilk Bay have been re-districted to numerous different elementary schools in the town.