New Castle is a town in Westchester County, New York, United States.

[3] It includes the named hamlets of Chappaqua and Millwood, but residents and businesses in the Town of New Castle can also have a designated city address of Ossining, or Millwood (together commonly referred to as the "West End" of New Castle) as well as Chappaqua or even Mt.

New Castle was originally inhabited by Native Americans, including the Siwanoy band of the Wappinger people.

Portions of New Castle were initially purchased in 1640 by Nathaniel Turner from Ponas Sagamore, chief of the Siwanoy.

In 1661, John Richbell purchased land, including all of present-day New Castle, from the Siwanoy.

[4] Two buildings from Horace Greeley's former farm are also on the National Historic Register, including the Greeley House, which houses the headquarters for the New Castle Historical Society, and Rehoboth, the first concrete barn in the country.

It is bordered by the towns of Bedford, Mount Kisco, and Somers to the northeast and Yorktown and Cortlandt to the northwest.