Northern boundary of Massachusetts
The northern boundary of the U.S. state of Massachusetts adjoins two other states: Vermont and New Hampshire. The majority of the line is roughly a straight line from the northwest corner of the state (42°44′44.7″N 73°15′54.13″W / 42.745750°N 73.2650361°W NAD27) east to a point in Dracut, just north of Lowell. East of that point, the border is a series of lines about 3 miles (5 km) north of the curving Merrimack River, ending in the Atlantic Ocean.
The 1629 charter of the Massachusetts Bay Colony gave the colony the land between the Merrimack River and Charles River. Specifically, the southern border was to be the line of latitude either 3 miles (5 km) south of Massachusetts Bay or 3 miles south of the southernmost bend of the Charles River, whichever was farther south. The northern border was to be 3 miles north of the northernmost bend of the Merrimack River. Between these lines of latitude the grant extended from the Atlantic to the Pacific. In 1629 the rivers had not been fully explored and the actual borders of the colony were uncertain. It turned out that the southernmost bend of the Charles is south of the southern curve of Massachusetts Bay. The line of latitude three miles south of the river's southernmost bend, approximately 42°2′ north, forms the basis of the southern border of Massachusetts to the present day. The Merrimack River turned out to originate farther north than expected, flowing south for most of its course and only turning eastward in its last several miles. Thus the 1629 grant gave the colony most of what is today New Hampshire and all of the original 1629 grant that formed the basis of colonial New Hampshire, but it took many decades before this was fully understood.
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