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.
According to the United States Census Bureau, the CDP has a total area of 5.7 square miles (15 km2). Plainview is on the Nassau County side of the border with Suffolk County. On the Nassau side it borders the hamlets of Hicksville, Old Bethpage, Syosset, and Woodbury. On the Suffolk side, its primary border is with Melville, but also touches West Hills.
Plainview's origins dates to 1648, when Robert Williams, a settler from Wales, bought land in the area. The land was considered desirable for farming because of a small pond named the Moscopas by local Native Americans, meaning "hole of dirt and water". The remainder of the land in the area was purchased by Thomas Powell in 1695 as part of the Bethpage Purchase. The name "Mannatto Hill" had already appeared on the 1695 deed of the Bethpage Purchase, and the settlement came to be called "Manetto Hill". Manitou was the Native American word either for "god" or for "spirit".
The 1837 arrival of the Long Island Rail Road to nearby Hicksville brought a boom to local farming. In 1885, residents of Manetto Hill petitioned the United States Postal Service for a local post office, but were turned down because, according to several accounts, a similar name was already in use upstate. The hamlet was then named "Plainview", for the view of the Hempstead Plains from the top of the Manetto Hills.