In 1716, Hardenbergh bought the immense tract of land since known as the "Hardenbergh patent", which covered some 2 million acres (8000 km²) of the Catskill Mountains in what is today Sullivan, Ulster and Delaware counties, from Nanisinos, sachem of the Esopus Indians, for the sum of 60 pounds. The purchase was subsequently confirmed and patent was granted to Hardenbergh and six others, although there were some disputes as to whether Hardenbergh's acquisition of the property had been truly legal. Indeed, in 1769 another former British officer, John Bradstreet, filed a claim to 50,000 acres (200 km²) based on that very assumption.
Shares in the patent changed hands frequently, and the terms under which the land was sold or leased were so varied and complex that it impeded settlement of the district and clouded the title to most of its tracts until well after the American Revolution. Even into the 20th century, many encumbrances remained.