The Equivalent Lands were several large tracts of land that the Province of Massachusetts Bay made available to settlers from the Connecticut Colony after April, 1716. This was done as compensation for an "equivalent" area of Connecticut-claimed territory which had been inadvertently settled by citizens of Massachusetts. The problem had arisen due to errors and imprecise surveys made earlier in the seventeenth century. The Equivalent Lands were never mapped.
The border between Massachusetts and Connecticut was first surveyed by the Massachusetts Bay Colony in 1642, following Springfield, Massachusetts' 1641 alliance with Boston. (Springfield left the fledgling Connecticut Colony during the late 1630s, following several disagreements with settlers from Hartford, Connecticut.)  For the next seventy-two years, Massachusetts (Springfield, in particular) controlled lands as far south as Warehouse Point at Windsor Locks, Connecticut - the northernmost point on the Connecticut River controlled by the tides. In the 1690s, Connecticut Colony officials performed their own survey, highlighting errors that were made in Massachusetts's 1642 survey.
When the boundaries between Massachusetts and Connecticut were cooperatively surveyed, beginning in 1713, it was found that large land grants that had been made available by Massachusetts Bay to Springfielders in the seventeenth century, 107,793 acres (436.22 km2) actually belonged to Connecticut. These settlers had established themselves in and about the towns of Springfield, Westfield, Suffield, and other areas west of the Connecticut River, believing themselves to be in lands belonging to the Massachusetts Bay Company.  Due to a change of jurisdiction that was unappealing to those already inhabiting the area, it was agreed that Massachusetts would retain administration over the settled lands, and in return, a grant of property ownership should be made to Connecticut of an equal number of acres, "as an equivalent to the said colony."
Creation and further development
The surveys laying out the new tracts were concluded on November 10, 1715. One tract was in the area around Pelham and Hadley, Massachusetts; another in the area encompassing modern day Putney, Brattleboro and Dummerston, Vermont; and another along the east side of the Connecticut River.
The commissioners appointed to locate these lands were: Joseph Dudley, Governor of Massachusetts; Gurdon Saltonstall, Governor of Connecticut; Elisha Hutchinson and Isaac Addington of Massachusetts; William Pitkin and William Whiting of Connecticut. The Equivalent Lands were then made available for purchase at Hartford on the 24th and 25th of April, 1716, with the proceeds from the sale going to the founding of Yale College. The lands were grouped in at least three parcels; however, no maps are extant of the Equivalent Lands–there may have been additional areas.
A group of four speculators purchasing a 44,000 acres (180 km2) parcel included a Bostonite, William Brattle, Jr. (for whom Brattleboro was named). Other initial purchasers of the lands included Paul Dudley, Thomas Fitch III, and Jonathan Belcher.
To defend the Massachusetts Bay Colony against Chief Gray Lock and others during Dummer's War, the Massachusetts General Court voted on December 27, 1723 to build a blockhouse and stockade north of its Northfield settlement in this parcel. Lieutenant-governor William Dummer signed the measure, and construction of Fort Dummer began on February 3, 1724. It was completed before summer. On October 11 of that year, the French attacked the fort and killed some soldiers. In 1725, Dummer's War ended. In 1728 the fort was converted into a trading post for commerce with friendly Indians. But in 1744, King George's War broke out, lasting until 1748. A small body of troops remained at the fort until 1750, after which it was considered unnecessary. The settlement surrounding the fort, "Brattleborough", was only scarcely populated until after the 1763 Treaty of Paris, when France finally abandoned the new world.
In 1752, a large section of the grant fell under the dominion of the new Province of New Hampshire, in a section now belonging to Vermont. The area making up the rest of the Equivalent Lands eventually fell under the control of other colonial entities based, in part, on the original royal charters. After many boundary permutations, the Equivalent Lands are now part of present day Vermont, New Hampshire, Connecticut and Massachusetts.
- Records held in office of the Secretary of the State of Connecticut; "Colonial Boundaries, Vol. III; Massachusetts, 1670-1827."
- Equivalent Lands; at Google Books.
- "The Equivalent Lands and Fort Drummer"
- Barrows, Charles Henry (1911). The history of Springfield in Massachusetts for the young: being also in some part the history of other towns and cities in the county of Hampden. The Connecticut Valley Historical Society. pp. 46–48.
- Vermont, The Green Mountain State Vol. 1; by Walter Hill Crockett; Century History Co.; 1921; pp 137-138.
- Note: There is a written description of the Equivalent Lands in the Connecticut Archives.
- An address, delivered at the opening of the new Townhall, Ware, Mass., March 31, 1847: containing sketches of the early history of that town, and its first settlers; at Google Books.
- A. J. Coolidge & J. B. Mansfield, ''A History and Description of New England;'' Boston, Massachusetts 1859. Books at Google.com.
- "Vermont, The Green Mountain State" Vol. 1; by Walter Hill Crockett; Century History Co.; 1921; p 252.
- Vermont, The Green Mountain State Vol. 1; by Walter Hill Crockett; Century History Co.; 1921; pp 278-280.