Sacketts had inhabited that part of Long Island since 1662 when Captain Joseph Sackett (1656-1719) moved to Newtown with his maternal grandfather. The Captain's son, Judge Joseph Sackett (1680-1755), amassed a fortune in land both on Long Island and in Orange County, west of the Hudson. The Judge's brother, John (1688-1728), and John's son, William (1727-1802), farmed the part of Judge Joseph's holdings which would later become the Kelly estate. William's son, Captain John Sackett (1755-1819) inherited the property from his father and it was from the estate of this John Sackett that the land and mansion passed into the hands of John A. Kelly.
The Sacketts were a large family. Over the decades from their mid-17th-century arrival in Massachusetts, they spread into the surrounding counties in Connecticut, New Jersey, and New York. The male heads of family became farmers, merchants, physicians, soldiers, magistrates, lawyers, masons, judges, ministers, and dealers in land. Those who settled within Newtown married the daughters and sons of other prominent families including the Leverichs, Fields, Lawrences, Moores, Alsops, Hazards, Kissams, and Bettses. In religion they were mostly Presbyterian or Anglican.
During the French and Indian Wars of 1754 to 1763, William Sackett and other Newtown residents Sacketts boarded French officers who had been captured and given liberty to move about "on parole."
Like other Queens residents, Sacketts found themselves on both sides of the rebellion against British rule. There was a William Sackett of Newtown, born in 1696, who was an officer in the Continental Army, while his nephew, our William Sackett — the one who farmed the Newtown property — was a Loyalist. James Riker says that during the summer of 1776 when the Continental Army was forced to retreat from Long Island, the rebel property owners were plundered by Loyalists and British soldiers. Many neighbors of the elder William were imprisoned and had their property confiscated. William himself was put under arrest in a place called the "corner house" in Newtown, but "contriving to make the guard drunk, he slipt away, and was not again called upon."
The Sacketts, like other Newtown residents, had family ties to the family of my great-grandmother, Annie Lefman Windmuller. Samuel Sackett was a cousin of the John Sackett, born 1755, who farmed in Newtown. Samuel lived nearby in Brooklyn where he married Elizabeth Kissam. Her family and the family of Annie's mother, Sarah Lenington Thorne, are interlinked in a couple of generations. I've written about this in an earlier blog post called Kissams.
Not long after it had been torn down a contemporary described the Sackett Mansion:
The mansion faced south at the foot Betts Ave. (today’s 58th St.) and along the old east-west Hurl Gate Road from Hallett’s Cove to Newtown village (today’s Woodside). The position of the mansion on the main highway gave it a commanding influence in eyes of military men. The mansion was the elite of colonial days, noted for its beauty and quaint old architecture. Surround the mansion were picturesque stretches of woodlawn, large cider houses, and sheep folds. The front door had 2 sections with a grand brass knocker, leading to the front hall that was 12 feet wide. The grand parlor on the right had was 17 feet each way, and on each side of the fireplace were two glass cases built in to the side walls, each on enclosed by an imitation gigantic sea scallop shell. The back room had a corner fireplace surmounted with closets. There were rooms on the other side of the hall and beyond them the kitchen with a spacious fireplace. There was a well in front of the house and in back a barn and a cider house. Nearby was a cemetery for slaves. The Sackett cider press was famous throughout Newtown where the Newtown pippin apples were abundant.
-- The History of the Sackett/Kelly/Howell Estate by Owen Clough who got it from "Old Newtown – Selections for the scrapbook originally written by the town clerk, William O’Gorman (1887)."
The annals of Newtown, in Queens county, New-York, containing its history from its first settlement, together with many interesting facts concerning the adjacent towns ; also, a particular account of numerous Long island families now spread over this and various other states of the union, by James Riker (D. Fanshaw, 1852)
The Founding Families of Woodside, Queens, New York by Owen Clough
The History of the Sackett/Kelly/Howell Estate by Owen Clough
The Sacketts of America, their ancestors and descendants, 1630-1907 by Charles H. Weygant, Vol 2 (Newburgh, N.Y. Journal print, 1907)
Biographical sketches of loyalists of the American Revolution by Lorenzo Sabine (Little, Brown, 1864)
The Sackett Family Association
The Sacketts of America on rootsweb
Descendants of Thomas Sackett on rootsweb
HISTORY OF QUEENS COUNTY with illustrations, Portraits & Sketches of Prominent Families and Individuals (New York: W.W. Munsell & Co.; 1882)
 Click the Woodside label at right to see these posts. Here are links to the two most recent of them:
(b) Capt. Joseph's son, Judge Joseph Sackett: "Judge Joseph Sackett was a man of probity, a Justice of the Peace and a Judge from 1749 to his death, Sept. 26, 1755, and it may be added that he was an office holder in the Presbyterian Church, took an active part in public affairs, and was ever held in high esteem by his townsmen." -- Sackett Family Association. In his will he left his son William "all my lands and Meadows in Newtown ... viz - My Mansion house and all the buildings and lot of ground they stand on, and all my lands on the east and south sides of the road that leadeth from Newtown to New York ferry ...." -- Sacketts of America
(c) Judge Joseph's brother, John Sackett (1688-1728): "John Sackett of Newtown, L. I., was married, Jan. 11, 1719, To Elisabeth Field, after whose death he was married to her sister, Susanna Field. They were the daughters of Elnathan Field, son of Robert Field, of Newtown, who was the son of Robert Field, a patentee of Flushing, L. I." -- Sacketts Of America. In his will he wrote: "I leave to my son William, all my lands and meadows, unless the child my wife now goes with shall be a son, in which case my lands are to be divided among them, allowing the buildings to the elder. If the child be a daughter, my son William shall pay her £60, when he is 21. If my son William dies without issue then I leave all my estate to my two daughters (not named). I make my two brothers, Joseph Moore and William Sackett, executors." -- Sackett on rootsweb
(d) John Sackett's son, William Sackett (1727-1802), "married, Feb. 14, 1749, Anne Lawrence, daughter of Capt. John Lawrence and his wife Patience Sackett. Mr. Sackett was by occupation a farmer and lived and died on the farm at Newtown on which he was born. (This William Sackett seems to have been a pronounced Loyalist, and if so, is unquestionably the William Sackett of Queens County, who acknowledged allegiance to King George in 1776, and is mentioned by Sabine as an addresser of Lt. Col. Sterling in 1779.)" -- Sackett on rootsweb
(e) William Sackett's son, Capt. John Sackett (1755-1819): "Mr. Sackett was a Revolutionary soldier. He served in the ranks of Col. John Harper's Levies and in other commands. After the war he took an active part in reorganization of the Militia, and in 1798 was commissioned First Lieutenant of Capt. Remson's Company of the Queens County Regiment, and served as such until 1793, when he succeeded Capt. Remson and commanded his company until 1804." -- Sackett Family Association
(f) Capt. John Sackett (1755-1819), son of William and Anna, m. Elizabeth Gibbs, of Conn., and remained in Newtown, where he d. May 12, 1819, in his 64th yr., and his widow, a. 71, May 27, 1836. Their ch. were William, b. Feb. 28, 1784, m. Gertrude, dau. of John Meserole, and d. Feb. 4, 1849; Lawrence, b. Sep. 14, 1786; Anna, b. Feb. 24, 1791, m. Peter Goreline ; Mary, b. Apr. 28, 1793, the widow of Jos. Lawrence; Patience, b. July 21, 1795; Elizabeth G., b. Dec. 18, 1799, and Amy L., b. Jan. 6, 1804. The last three d. single. -- Sackett Family Association
 Actually their fathers were cousins so they were technically second cousins or cousins once removed (I forget which is right). The author of a page on William Sackett found on rootsweb says "William Sackett was by occupation a farmer and lived and died on the farm at Newtown on which he was born. (This William Sackett seems to have been a pronounced Loyalist, and if so, is unquestionably the William Sackett of Queens County, who acknowledged allegiance to King George in 1776, and is mentioned by Sabine as an addresser of Lt. Col. Sterling in 1779.)"
 The "corner house" was an inn belonging to Samuel Fish. My source is The annals of Newtown, in Queens county, New-York, containing its history from its first settlement, together with many interesting facts concerning the adjacent towns ; also, a particular account of numerous Long island families now spread over this and various other states of the union, by James Riker (D. Fanshaw, 1852)