Chatham, town, Barnstable County, southeastern Massachusetts, on Cape Cod, on the Atlantic Ocean; incorporated 1712. Chatham is a residential and resort town with a large retirement community, situated at the southern end of Cape Cod National Seashore. Fishing is an important industry. Settled in 1656, the community is named for the British statesman William Pitt, 1st Earl of Chatham. Population 6,071 (1980); 6,579 (1990); 1,937 (1996 estimate).