About US ZIP Codes

The ZIP Code system, also known as the Zone Improvement Plan Code, is a postal code system used in the United States to help facilitate the efficient delivery of mail. This system was introduced in 1963 and has been a crucial component of the United States Postal Service ever since. The ZIP Code system is comprised of five-digit codes, with an optional four-digit extension that can further refine the location of the address. The first three digits of the ZIP Code represent a sectional center facility (SCF) that serves a particular geographic region. The fourth and fifth digits represent smaller post offices or delivery zones within the SCF area. The ZIP Code system was developed in response to the growing volume of mail being sent and delivered throughout the United States. Prior to the introduction of the ZIP Code system, mail was sorted and delivered using a combination of city, state, and street address information. This process was often slow and inefficient, resulting in delays and lost mail. With the introduction of the ZIP Code system, mail could be sorted and delivered more quickly and accurately. The use of ZIP Codes also made it easier to track and monitor mail delivery, which helped to reduce lost or delayed mail.

ZIP Code Geography

There are several types of US ZIP Codes:

Standard (also known as non-unique) ZIP codes usually do not cross state lines but they do cross city and county lines. There are a couple exceptions to the state line rule: One example is ZIP code 42223 which is shared between Kentucky and Tennessee. For ZIP Codes within a US State we provide data on all counties, cities, neighborhoods and school districts within it's area. For certain areas where we currently have data we also provide school attendance area information.

First Level US ZIP Code Map
Level 1 ZIP Code Zones

The US ZIP Code system is divided into 10 zone which represent the first digit in each ZIP Code (0 to 9). These zones are regionally based with 0 in the Northeast increasing westward with 9 in the Western US and pacific.

First Level US ZIP Code Map
Level 2 ZIP Code Zones

At the 2 digit level ZIP Codes can be further refined geographically.

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