Following the American Revolution, western New York was opened up for development as soon as New York and Massachusetts compromised and settled their competing claims for the area in December 1786 by the Treaty of Hartford. The compromise was that, while New York would have sovereignty over the land, Massachusetts would have the "pre-emptive" right to obtain title from the Indians.

After a great deal of machinations by various speculators, on April 1, 1788, the entire Massachusetts preemptive right -- comprising some 6,000,000 acres -- was sold to Oliver Phelps and Nathaniel Gorham, both of Massachusetts. The sales price was $1,000,000, payable in three equal annual installments of certain Massachusetts securities then worth about 20 cents on the dollar. This sale was of the preemptive right for all land west of a line running from the mouth of Sodus Bay on Lake Ontario, due south through Seneca Lake, to the 82nd milestone on the Pennsylvania border near Big Flats (the "Pre-emption Line") all the way to the Niagara River and Lake Erie. Phelps and Gorham would not, however, own the land in fee until they extinguished all Indian titles.

Phelps and Gorham wasted no time in exploiting their purchase. On July 8, 1788, by the Treaty of Buffalo Creek, they extinguished Indian title to all land from the Pre-emption Line west to the Genesee River, as well as to lands west of the Genesee running south from Lake Ontario approximately 24 miles and extending west from the river approximately 12 miles, with this western boundary paralleling the course of the Genesee. (This 184,300 acre tract west of the Genesee was known as The Mill Yard Tract, so named because Phelps and Gorham asked the Indians for land west of the Genesee at the Falls so they could bill a sawmill and gristmill.) For this extinction of title, Phelps and Gorham paid the Indians $5,000, plus an annuity of $500. The area to which title was extinguished comprised some 2,250,000 acres.

The preemptive right to remaining lands of the Phelps and Gorham Purchase west of the Genesee River, comprising some 3,750,000 acres, reverted back to Massachusetts due to the failure of Phelps and Gorham to extinguish Indian title and make the 1790 payment. Massachusetts then re-sold the pre-emptive right to those lands to Robert Morris in 1791 for $333,333,33. At that time, Morris was the richest man in America, as well as a signer of the Declaration of Independence, and financier of the American Revolution. In September 1791, Morris extinguished the remaining Indian title for all the lands west of the Genesee at the "Treaty of Big Tree" (Geneseo) Morris then re-sold most of these lands in 1792 and 1793 to the Holland Land Company (known as The Holland Purchase). Morris reserved for himself the remainder of these lands, which was about 500,000 acres in a twelve mile wide strip along the east side of the Holland Purchase, from the Pennsylvania border to Lake Ontario, known as as The Morris Reserve. At the north end of the Morris Reserve, a 87,000 acre triangular shaped tract (the "The Triangle Tract") was sold by Morris to Herman Leroy, William Bayard and John McEvers, while a 100,000 tract due west of the Triangle Tract was sold to the State of Connecticuit.