Kings Park is a hamlet and census-designated place in the Town of Smithtown, in Suffolk County, on Long Island, in New York, United States. The population was 17,282 as of the 2010 census. Its rela…Kings Park is a hamlet and census-designated place in the Town of Smithtown, in Suffolk County, on Long Island, in New York, United States. The population was 17,282 as of the 2010 census. Its relative tranquility prompted it to be the site of the Kings Park Psychiatric Center instead of New York City.