Eastham is a town in Barnstable County, Massachusetts, United States, Barnstable County being coextensive with Cape Cod. The population was 4,956 at the 2010 census.
For geographic and demographic information about the village of North Eastham, please see North Eastham, Massachusetts.
According to the United States Census Bureau, the town has a total area of 25.7 square miles (66.6 km2), of which 14.0 square miles (36.2 km2) is land and 11.7 square miles (30.4 km2), or 45.68%, is water. It is bordered by Cape Cod Bay and the Atlantic Ocean on its western and eastern sides, respectively. Eastham is also bordered by the towns of Wellfleet and Orleans on its northern and southern sides, respectively. Eastham is located on the "forearm" of Cape Cod, and is 23 miles (37 km) south of Provincetown, the same distance east-northeast of Barnstable, 38 miles (61 km) east of the Sagamore Bridge, and 92 miles (148 km) (by land) southeast of Boston.
Approximately one-third of the town is located within the Cape Cod National Seashore. There are several freshwater ponds near the center of town, the largest being called Great Pond, which has two public beaches. Powerboats with 50 and under horsepower motors are allowed on Great Pond and Herring Pond, with water skiing only permitted at Great Pond on even numbered days. Along the Atlantic coast, portions of the CCNS include several islands, divided by channels which lead from Nauset Bay and Salt Pond Bay to the ocean. The town also shares Town Cove with neighboring Orleans. Several creeks and the Herring River run inland from the bay side.