Complex sentence: It is the name given to the winter residence (and subsequently the tribe itself) of the group of Massachusett Indians which lived at the mouth of the Neponset River in summer, and is now contained almost entirely by the town of Canton, Massachusetts.
Split into simpler sentences: It is the name given to the winter residence (and subsequently to the tribe) of the group of Massachusett who lived at the mouth of the Neponset River in summer. Ponkapoag is now contained almost entirely by the town of Canton, Massachusetts.