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The U.S. Postal code, more commonly referred to as ZIP code or Zoning Improvement code, is made up of a primary 5 digit numerical code. There is a ZIP+4 code, mainly used by the Post Offices and businesses in the US, in which case you would have the primary 5 digit ZIP code and then add a 4 digit secondary numerical code, separated by a hyphen or dash.

Breaking down the ZIP Code Edit

Primary State Prefixes Edit

The first digit of the ZIP code (Nxxxx) is allocated as follows:

Secondary Regional Prefixes Edit

The next two digits (xNNxx) represent the sectional center facility (e.g. 477xx = Vanderburgh County, Indiana), and the fourth and fifth digits (xxxNN) represent the area of the city (if in a metropolitan area), or a village/town (outside metro areas): 47722 (4=Indiana, 77=Vanderburgh County, 22=University of Evansville area). When a sectional center facility's area crosses state lines, that facility is assigned separate three-digit prefixes for the states that it serves.

  • Despite the geographic derivation of most ZIP codes, the codes themselves do not represent geographic regions; in general, they correspond to address groups or delivery routes. As a consequence, ZIP code "areas" can overlap, be subsets of each other, or be artificial constructs with no geographic area (such as 095 for mail to the Navy  wp, which is not geographically fixed). In similar fashion, in areas without regular postal routes (rural route areas) or no mail delivery (undeveloped areas), ZIP codes are not assigned or are based on sparse delivery routes, and hence the boundary between ZIP code areas is undefined. For example, some residents in or near Haubstadt, Indiana, which has the zip code 47639, have mailing addresses with 47648, the ZIP code for neighboring Fort Branch, while others living in or near Fort Branch have addresses with 47639. Many rural counties have similar logistical inconsistencies caused by the aforementioned sparse delivery routes, often known as Rural Routes or by some other similar designation.
  • In rare circumstances, a locality is assigned a ZIP code that does not match the rest of the state; in other words, a ZIP code may cross state lines. In general, the locality is so isolated that it is most conveniently served from a sectional center in another state.

3-digit ZIP code prefixes Edit

0xx codes | 1xx codes | 2xx codes |3xx codes | 4xx codes | 5xx codes | 6xx codes | 7xx codes | 8xx codes | 9xx codes