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The US History of the Zip Code or Zone Improvement Plan

A government system which started in the earyl 1960's that uses 5-digit numbers (codes) to identify each individual post offices or delivery stations in city areas associated with an address is the definition of ZIP (Zone Improvement Plan) Code

Zip Codes are used for tracking of mail and collecting geographical statistics in the United States. The U.S. Census Bureau uses data that includes the latitude and longitude of the center-point of some ZIP codes. The Census Bureau does not keep up-to-date datasets of all Zip Codes. Complete datasets are commercially available.

Many Zip Codes are for towns and Villiages, census-designated places, portions of cities, or entities that are not municipalities. The postal designations for place names become de facto locations for their addresses, and as a result it is difficult to convince residents and businesses that they actually are located in another city or town different from the "default" place name associated with their ZIP codes. Because of the confusion and lack of identity generated by this situation, some cities have successfully petitioned the Postal Service to change ZIP-code boundaries or create new ZIP codes so that their cities can be the "default" place name for addresses within the ZIP code.

This mis understanding also can have financial implications for local county governments, because the volume of mail is among the factors used by the Census Bureau to estimate population changes between decennial census enumerations. Sometimes local officials in a community that is not the default place name for a zip code but is an acceptable place name will advise residents to always use the name of the community, because if the census estimate of that towns population is low they will get fewer State and Federal funds that are computed based on population.

Acceptable place names come into play in areas of the country where many citizens identify more strongly with a particular urban center than the municipality they actually live in. For example, Allegheny County, Pennsylvania has 130 distinct municipalities, but many of the county's residents, and even residents of adjacent counties, commonly use "Pittsburgh, PA" as their postal address. The same thing applies in many cities that have more than one zip code.

Rarely, a locality is assigned a ZIP code that does not match the rest of the state. This is when the locality is so isolated that it is served from a sectional center in another state. For example, Fishers Island, New York, bears the ZIP code 06390 and is served from Connecticut all other New York ZIP codes begin with 1. Similarly, some Texas ZIP codes are served from New Mexico and thus bear codes beginning with 8 rather than 7. Returned government parcels from the District of Columbia are sent to ZIP codes beginning with "569", so that returned parcels are security checked at a remote facility (this was put into place after the anthrax scare).

To learn more about our ZIP Code finder - US ZIP Code Database Lists with Demographics Information.