Plainview is a hamlet and census-designated place located near the North Shore of Long Island in the town of Oyster Bay in Nassau County, New York, United States. The population of the CDP as of 2020 was 27,100. The Plainview post office has the ZIP code 11803.Plainview and its neighboring hamlet, Old Bethpage, share a school system, library, fire department, and water district. Law enforcement for the communities is provided by the Nassau County Police Department's Second Precinct.