The Province of Massachusetts Bay was a colony in New England which became one of the thirteen original states of the United States. It was chartered on October 7, 1691, by William III and Mary II, the joint monarchs of the kingdoms of England, Scotland, and Ireland, and was based in the merging of several earlier British colonies in New England. The charter took effect on May 14, 1692, and included the Massachusetts Bay Colony, the Plymouth Colony, the Province of Maine, Martha's Vineyard, Nantucket, Nova Scotia, and New Brunswick; the Commonwealth of Massachusetts is the direct successor. Maine has been a separate state since 1820, and Nova Scotia and New Brunswick are now Canadian provinces, having been part of the colony only until 1697.

Massachusetts, officially the Commonwealth of Massachusetts, is a state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and Gulf of Maine to its east, Connecticut and Rhode Island to its south, New Hampshire and Vermont to its north, and New York to its west. Massachusetts is the sixth-smallest state by land area. With over seven million residents as of 2020, it is the most populous state in New England, the 16th-most-populous in the country, and the third-most densely populated, after New Jersey and Rhode Island.