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:
- 0 = Connecticut (CT), Massachusetts (MA), Maine (ME), New Hampshire (NH), New Jersey (NJ), Puerto Rico (PR), Rhode Island (RI), Vermont (VT), Virgin Islands (VI), Army Post Offices in Europe (AE) and Fleet Post Offices in Europe (AE)
- 1 = Delaware (DE), New York (NY) and Pennsylvania (PA)
- 2 = District of Columbia (DC), Maryland (MD), North Carolina (NC), South Carolina (SC), Virginia (VA) and West Virginia (WV)
- 3 = Alabama (AL), Florida (FL), Georgia (GA), Mississippi (MS), Tennessee (TN), Army Post Offices in the Americas (AA) and Fleet Post Offices in the Americas (AA)
- 4 = Indiana (IN), Kentucky (KY), Michigan (MI) and Ohio (OH)
- 5 = Iowa (IA), Minnesota (MN), Montana (MT), North Dakota (ND), South Dakota (SD) and Wisconsin (WI)
- 6 = Illinois (IL), Kansas (KS), Missouri (MO) and Nebraska (NE)
- 7 = Arkansas (AR), Louisiana (LA), Oklahoma (OK) and Texas (TX)
- 8 = Arizona (AZ), Colorado (CO), Idaho (ID), New Mexico (NM), Nevada (NV), Utah (UT) and Wyoming (WY)
- 9 = Alaska (AK), American Samoa (AS), California (CA), Guam (GU), Hawaii (HI), Marshall Islands (MH), Federated States of Micronesia (FM), Northern Mariana Islands (MP), Oregon (OR), Palau (PW), Washington (WA), Army Post Offices in the Pacific (AP) and Fleet Post Offices in the Pacific (AP)
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.
- In most urban areas, like 462 for Marion County, Indiana, the three-digit prefix will often exist in one county, while, in rural and most suburban areas, the prefix will exist in multiple counties, for example, the neighboring 476 prefix is found in part or in entirely in six counties: Gibson, Pike, Posey, Spencer, Vanderburgh and Warrick. In some cases, an urban county may have more than one prefix. This is the case with Allen (467, 468), Lake (464, 463), St Joseph (465, 466) and Vanderburgh (476, 477) counties. Cities like Chicago, Houston, Los Angeles and New York have multiple prefixes within their city limits.
- 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 , 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.