The area of the Kensico Reservoir between Old Orchard Street in North White Plains and adjacent Valhalla was formerly Native American territory under the rules of Sachem Pathungo and Cockensenko.

After the Siwanoy leaders, the original custodians of the land, sold the territory to European settlers, the small farming community about 30 miles north of New York City evolved into a new settlement called Wright's Mills. It was named after the Wright brothers: Thomas, who piloted a sawmill in modern-day Armonk, and Reuben, who operated a gristmill near the Bronx River next to the modern-day Kensico Dam Plaza.

During the American Revolution, the tranquil farming community played a pivotal role, serving as a base for the Continental Army. This strategic location, however, made it a target for numerous attacks from Loyalist groups aligned with the British Army, including a deadly skirmish with Johann Althouse's Sharpshooters.

In July 1778, the Patriots increased their defenses at Wright's Mills as it became the Revolutionary War headquarters of General George Washington, who had previously stayed there following the October 1776 Battle of White Plains.

During the Revolutionary War, the Wright brothers' barns became hallowed ground. One of these barns housed Continental Army General Charles Lee after he was court-martialed for treason in 1778, and later, it was where the Continental Army held British spy Major John Andre captive in 1780 after several Patriots apprehended him in nearby Tarrytown, NY, after his infamous secret meeting with General Benedict Arnold.

During the eighteenth century, Wright's Mills underwent at least four name changes, including Sands Mills and Knowlton Mills, before 1850, when local businessman Jonathan Washington Tompkins suggested the village stop naming itself after the local miller and instead be permanently named Kensico, after Siwanoy sachem Cockensko.

The village's post office and new train station along the Metro North line adopted the Kensico name, which gave the growing community a sense of pride and identity. The addition of the train line helped local businesses like its multiple dairy farms, mills, factories, and shops like Wykoff's Store thrive however,a series of train accidents caused numerous cases of death and dismemberment.

A century after the Revolutionary War ended, Kensico had a population of around 200 people. Despite the village not having electricity or running water, it had a lot of establishments that served liquor, which led to an increase in crime from drunken burglars and troubles with drunken tramps, including one case when some drunken hobos accidentally lit themselves on fire in a barn, another where a bum named "McGowan" attacked a local dairy farmer, and a near-deadly incident at the Joseph Reevs Hotel, where in 1884, four intoxicated workers of the original earthen Kensico Dam attacked the bartender, Samuel Robbins, with clubs and a knife, leaving him with a fractured skull.

Around this time, a ferocious panther broke away from a traveling circus and terrorized the village. Locals spotted it near Wampus Swamp, by The Raven Hotel, and even near St. Mary's Lake (now Silver Lake near Buckout Road), leaving a trail of destruction. Its unclear if it was ever caught.

Albert Montfort operated a grocery store out of the bottom floor of his house in Kensico Village. In December 1871, his young daughter Albertina, six-year-old niece Carrie May, and ten-year-old nephew George Patterson went ice skating on a nearby frozen millpond. The ice, however, collapsed, and the children drowned.
Several years later, in 1879, Albert and his wife Anne separated. A few months after the separation, the then 50-year-old grocery store owner remarried Emma Jean Reynolds, a local 19-year-old.

In September 1882, a local baker, George Mead, found Albert lying dead on his kitchen floor in a pool of blood. Someone had fatally attacked him in such a violent way with an ax, nearly severing his head from his body and leaving multiple gashes on his skull. The police have yet to formally charge anyone in the murder of Albert Montfort, which remains the oldest cold case in the history of Westchester County.

The book The Lost Village Of Kensico reexamines the case. It looks at multiple suspects, including Albert's first wife, who filed for his property, claiming they never actually got divorced his second wife, Emma, who had already remarried by the time the court decided what to do with Albert's estate, Emma's brother Charlie, who the police suspected but didn't charge because he was in jail for another crime, and Emma's stepfather, Wesley Stillson, who the villagers publically accused of the murder and who shortly after mysteriously died of "heart disease." Despite the crime scene now submerged under the depths of Kensico Reservoir, perhaps you can help solve the case and bring justice to murder victim Albert Montfort.

By 1905, New York City was increasingly fearful of drought and disease and required even more water than the original earthen Kensico Reservoir could provide. The city needed a larger water supply and quickly won approval from the state legislature to take the land required for the project from the village of Kensico.

The new dam, a force of nature, would engulf the Rye Ponds entirely and swallow up almost all the hillside farms. The floodwaters would erase churches, schools, stores, and homes from the village's landscape. The crossroads where George Washington's officers convened, the barn where The Continental Army held Charles Lee and Major Andre, and the house George Washington used as a Revolutionary War headquarters would all be lost to the depths.

By the end of 1909, Kensico's population had dwindled, and by the end of the year, Jacob Pfister permanently closed the Kensico post office. The Kensico Dam project required building lots of tiny temporary homes, called camps, near the work site to accommodate nearly 2,000 workers and their families. Many of these camps sprung up nearby on North Broadway and Cloverdale Avenue in White Plains. On the west side of the lake, an additional site, Camp Columbus, had 43 more buildings to support 500 workers.

By the end of 1910, New York City had acquired all of the land that would become the Kensico Reservoir. One of the first projects for the workers was to drain and fill a large swamp to form the present Kensico Dam Plaza. In November 1912, quarry workers set off fifteen tons of dynamite in one massive blast at the stone quarry on Old Orchard Street. They blew up the quarry to provide stone for the dam construction.

On a tragic day in April 1915, a premature dynamite explosion in a trench at the Kensico Dam site killed eight Italian workers and injured nearly a dozen more.

Workers completed the Kensico Dam in 1917 for an estimated total cost of $15 million (approximately $319M in 2024). The dam is 1,825 feet long, stands 307 feet above its foundation, and contains 1,000,000 feet of masonry. It is capable of holding back about 30 billion gallons of water and is used to provide residents of Westchester County and New York City with their drinking water. The enormous size of the Kensico Dam is comparable to the amount of masonry used in building some Egyptian pyramids.

While some may dismiss the claim, rumors from local fishermen persist that when the reservoir water levels are low, you can sometimes glimpse the shadowy steeple of Kensico's little Methodist church, surrounded by its never exhumed burial ground, reaching up from the depths.

Some blame Kensico's treacherous history and inevitable doom on an ancient Native American curse. According to legend, the settlers who purchased the land agreed not to disturb its white wood trees, which the Siwanoy held sacred and used for numerous things, including making canoes. However, the "White Man" broke the pact and began destroying the trees, often burning them as firewood. Some believe their actions triggered the curse of promised doom. Some even say that the spirits of Pathungo and Cockensenko watched over their former land where they are rumored to be buried, at the peak of what was once Archer's Hill, now surrounded by the man-made waters of Rye Lake, on what is now known as Great Island.