Riverhead Post Office is a United States post office located at 1210 West Main Street in Riverhead, New York. It serves the ZIP code 11901, covering all of Riverhead, along with Roanoke, Reeves Park, Centerville, northern Jamesport, and northwestern Laurel. As with Patchogue and Smithtown's Village of the Branch, Riverhead Post Office was known as a source for obscure postal denominations by Long Island-based stamp collectors. The building was added to the National Register of Historic Places in 1989.