Windsor is a small historic unincorporated community and census-designated place located within Robbinsville Township in Mercer County, in the U.S. state of New Jersey. The area is served as United States Postal Service ZIP Code 08561. As of the 2020 United States census, the CDP's population was 330, an increase of 104 above the 226 counted at the 2010 census. The community, covering 570 acres, was added to the National Register of Historic Places in 1992.