<P> This also occurs in some rural areas where portions of one town have their mail delivered to other post offices . For example, while most of the town of Plainfield, Massachusetts is in ZIP Code 01070, some sections of town are in the ZIP Code area for the neighboring town of Cummington with ZIP Code 01026 . Only the preferred name of Cummington is allowed in ZIP Code 01026, so residents of parts of Plainfield must list their address as being in Cummington . </P> <P> This phenomenon is repeated across the country . The previously mentioned Englewood, Colorado is an inner - ring suburb that was built out by the 1960s . Its post office served the area that is now the high - growth southern tier of the Denver metropolitan area, and ZIP Codes in this area were assigned Englewood as their preferred place name . A business community as large as downtown Denver has grown in this area, with headquarters for many internationally recognized corporations . These companies indicate Englewood as their location (the preferred postal place name), although they are located in other cities . As a result, there are really two Englewoods--the city, small and with a largely working - class residential population, and, a number of miles away, the postal Englewood, a vast suburban area of upscale subdivisions and office parks that have nothing to do with the city of Englewood yet share a split identity with it solely because of ZIP Codes . People who say they live or work in Englewood and identify closely with it may rarely enter the city . In Indiana, the ZIP Code for a town usually indicates the ZIP Code for its corresponding township, as nearly all of Indiana's small town post offices have rural routes . </P> <P> Acceptable place names also come into play in areas where citizens identify more strongly with a particular urban center than their own municipality . For example, Allegheny County, Pennsylvania, has 130 distinct municipalities, yet many of the county's residents, and even some residents of adjacent counties, commonly use Pittsburgh, Pennsylvania as their postal address . On the opposite end of the spectrum, in some urban areas, neighborhood names may be acceptable even though they have no legal standing, such as La Jolla, California, which is the preferred place name for ZIP Code 92037, despite the fact that La Jolla is a district of San Diego, California and not a separate legal entity (this ZIP Code is also in the 919 / 920 sequence used by San Diego County's suburban and rural areas, not in the 921 sequence used in the remainder of the City of San Diego, even though La Jolla has always been part of San Diego). </P> <P> Many ZIP Codes are for villages, census - designated places, portions of cities, or other entities that are not municipalities . For example, ZIP Code 03750 is for Etna, New Hampshire, but Etna is not a city or town; it is a village district in the town of Hanover, which itself is assigned the ZIP Code 03755 . Another example is ZIP Code 08043, which corresponds to the census - designated place of Kirkwood, New Jersey, but serves the entirety of Voorhees Township . This is also the case in LaGrange, New York, a portion of which is served by the 12603 ZIP Code based in the neighboring town of Poughkeepsie . The rest of LaGrange is served by the LaGrangeville Post Office . LaGrangeville is itself not a town at all, but a section of LaGrange . Willow Grove, Pennsylvania, served by the 19090 ZIP Code, is a village that straddles the border of Upper Moreland Township and Abington Township, and that post office also serves a small portion of Upper Dublin Township . Furthermore, non-municipal place names may also share ZIP Codes with municipal place names . For example, West Windsor Township, New Jersey, is commonly referred to in most mailing databases as Princeton Junction, a census - designated place within West Windsor . Silver Spring, Maryland, (20815, 20901--20912) is neither a city nor a town, but simply the common name for an unincorporated area consisting of a large part of the lower southern portion of Montgomery County . </P>

Why does the zip code have two boxes