Originally, it was a 86,000-acre (35,000 ha) tract stretching from the Hudson River on the west to the first boundary line between the Province of New York and the Colony of Connecticut, on the east, twenty English miles in length by ten in width, in shape nearly a rectangular parallelogram, forming, "The Manor of Cortlandt."

[16] Mrs. Gertrude Beekman, one of the original heirs of the first Lord of the Manor, died on March 23, 1777, leaving what was known as the "Peekskill estate" to her great nephew, Pierre's son Gilbert L. Van Cortlandt.

It comprised that part of the manor lying on the river from the line of Putnam County and two tracts of land in Peekskill being about 340 acres, embracing Anthony's Nose, Roa Houk, Annsville and the large estate on which, in later years, was the residence of Pierre Van Cortlandt, Jr., where a spacious mansion [Oldstone, discussed below] was probably built about 1769.

The old brick mansion [Upper Manor House] erected A. D. 1773, occupies a very sequestered and romantic spot on the north side of the post road, immediately above the vale of Annsville.

"[18] In 1749, Pierre turned the family's simple hunting lodge into an elegant residence known as Van Cortlandt Manor House, adding the upper stories and porches.

[22] Between 1756 and 1773, Pierre Van Cortlandt built and enlarged a home along the Albany Post Road, in Cortlandtville, a suburb near Peekskill, Westchester County, New York known as the Upper Manor House.

[26] The accompanying graphics show the proximity of the Upper Manor House to Van Cortlandt's home, Oldstone, on the buff of Anthony's Nose, overlooking the site where the Fort Independence Hotel once stood.

His son, Philip, wrote in his memoir that in "the Spring of 1780 ... having passed thro the Manor of Cortlandt Saw My friends at Peeks Kill and then to Nine Partners where my Father and his family were obliged to remove from Rhinebeck as Colo. Livingston would not suffer him to remain any longer".

[30] Van Cortlandt served in the colonial forces during the American Revolution in spite of efforts by British officials to ensure his loyalty to Great Britain.

By the end of 1776, the British Army, aided by loyalist groups, control Manhattan, Long Island, and lower Westchester County, while American forces were stationed in the region north of the Croton River around Peekskill.

Farmers developed a clandestine cattle trade New York City, where such animals brought a high price in specie or in British notes rather than in questionable trouble paper.

[35]Only once was she prevailed upon to leave her residence, being persuaded by her brother, Colonel Philip Van Cortlandt, to retire with her family some miles back in the country for safety from a scouting party on their way from Verplanck's Point.

A historian wrote that upon Cornelia's return: Not an article of furniture was left, except a bedstead; a single glass bottle was the only drinking utensil; and one ham was all that remained of the provisions, having by good fortune, been hung in an obscure part of the cellar.

Soon after, she was called upon by two of the American officers — Putnam and Webb — who asked how she had fared, not supposing she had been visited with annoyance, and were much surprised at her description of the state of the house on her return.

While residing there, Cornelia (Van Cortlandt) Beekman refused to give a representative of the British spy John André an American officer's uniform she had in safe-keeping.

Smith replied that Webb had no time to write one, adding: "You know me very well, Mrs. Beekman and when I assure you that Lieutenant Jack sent me for the valise, you will not refuse to deliver it to me, as he is greatly in want of his uniform."

Smith was angry at her doubts, and appealed to her husband, urging that the fact of his knowing the valise was there, and that it contained Lieutenant Jack's uniform, should be sufficient evidence that he came by authority; but his representations had no effect upon her resolution.

He and Major André were of the same stature and form; "and beyond all doubt", says one who heard the particulars from the parties interested, "had Smith obtained possession of the uniform, Andre would have made his escape through the American lines.

"[36] Cornelia Van Cortlandt, Pierre's oldest daughter, and her husband Gerard G. Beekman, left New York City in early 1776 for the Manor House at Croton, but this was too near the neutral ground to be a safe refuge for her father and family, and it behooved that ardent patriot to keep out of reach of his enemies, many of whom were his own tenantry, now ranged against their country.

A curious old journal tells of their exodus, and the catalogue of the flocks and herds, man-servants and maid-servants that were sent to Rhinebeck, reads like a biblical story of the journeyings of the Patriarchs.

[30] Not only did George Washington sleep at the Van Cortlandt Upper Manor House, he stayed for extended periods commanding the battles of Long Island, New Amsterdam, and Westchester County.

[41] In August 1776, at the foot of Anthony's Nose, Fort Independence was built on his father's land, on the north bank of the Annsville Creek as it empties into the Hudson River.

[43][44] On the opposite side of Annsville Creek [north of Peekskill] at the point known as Roa or Roay and formerly Roya Hook, stood the old Revolutionary Fort Independence.

Pierre thus added his name to the list of those who sought to unseat George Clinton, who led the New York forces opposed to ratification of the Federal Constitution of 1787.

From February to July, 1789, with George Clinton, Egbert Benson, John Hathorn, Peter Gansevoort, Jr., Ezra L'Hommedieu, and Samuel Jones, Van Cortlandt met with a number of Chiefs of the Cayuga Nation in an effort to legalize New York's claims to lands formerly held by the Iroquois Confederation.

It was resolved, "that the treasurer and secretary of this Congress be and they hereby are directed forthwith to repair, with all and singular the public papers and money now in their custody or possession, unto the White Plains, in the county of Westchester.

The bugler would sound halt; they would wheel their horses into a hollow square; there put through legislation in approved parliamentary style, and announce adjournment by the bugle call, when they would break into fours and proceed on their way.

For the various proofs of confidence and regard with which you have honored me for a long series of years, I return you my cordial thanks-and I trust that if I have ever omitted to manifest a proper sense of your favors, it has never proceeded from design.

"[61] The following obituary notice appeared in the Albany Gazette of May 17, 1814: Pierre Van Cortlandt, early took an active part against every oppression of the English government upon the colonies.

In the year 1795 he declined a re-election as lieutenant governor, and retired into private life.An obituary published in the New York Commercial Advertiser, prepared by his sons, paid homage to the father with the apt summation that Pierre Van Cortlandt was, "a patriot of the first order zealous for the Liberties of his Country.