According to the 2000 U.S. Census, residents of the Town of North Castle have reached 10,849 in total. This was an increase of 7.8% or 788 people since 1990, when North Castle's population was 10,061.

The Town of North Castle comprises approximately 26 square miles and is situated at the narrow waist of Westchester County where the corner of the State of Connecticut extends west toward the Kensico Reservoir. The bulk of the Town's land area lies north of this corner, but the most densely populated part of the Town lies to the south. The Kensico Reservoir separates these two parts of North Castle.

The Town has been divided into three distinct geographic areas: North White Plains, Armonk, and the Eastern District (the hamlet area in the Eastern District is referred to as Banksville). North White Plains is the most urban portion of the Town. The Eastern District retains its low-density residential character.

The seat of Town government is located in Armonk. This is why North Castle is often referred to as Armonk though the town has other equally beautiful and thriving locations including the hamlets of Banksville, North White Plains and Middle Patent in its area of 26 square miles.

Along King Street one can easily find the 400-acre world headquarters of IBM Corporation. IBM is Westchester's largest private employer, with about 9,000 workers. Besides IBM, North Castle also has in its distinguished roster of conglomerates Swiss Re and the Municipal Bond Insurance Association. Municipal Bond bought land on Cooney Hill to make way for additional corporate space. These corporations help keep residential property taxes down, as does New York City, which also owns 3,000 acres in North Castle, including the Kensico Reservoir.

North Castle is steeped in American history. Before the town was established in 1730, the Siwanoy people of the Algonquin tribe inhabited the area. English farmers later settled in the area.

The area quickly became a refuge for people fleeing from religious persecution. People from Massachusetts and Connecticut settled the eastern part of North Castle, while Quakers from Rye and Long Island gathered in Armonk. By 1730, North Castle was an established settlement.

Place Names

Many of North Castle’s locations were named after the Native Indian sachems (or chiefs): Wampus Pond and stream from Sachem Wampus, Mianus Gorge and River from Sachem Mayano, Kensico Reservoir and the lost village of Kensico from Sachem Cokenseko, and Coman Hill School from Sachem Cohamong.

North Castle's name is said to derive from a barrier built by the Mohican people to protect themselves from enemy attacks. This stood on the same hill where the IBM Headquarters can be found. The site was called "North Fort" and later, because early settlers felt it resembled a castle, it became "North Castle".