Zip Code Lookup

About US Zip Codes

ZIP codes (Zone Improvement Plan codes) were introduced by the United States Postal Service in 1963 to improve mail delivery efficiency. Today, there are over 42,000 active zip codes across the United States, each serving a specific geographic area.

The first digit of a zip code represents a broad geographic region, starting with 0 in the Northeast and increasing as you move west, with 9 covering the West Coast, Alaska, and Hawaii. The next two digits narrow the area further, and the final two identify a specific post office or delivery zone.

ZIP+4 codes add a four-digit extension to provide even more precise delivery information, typically identifying a specific city block, apartment building, or individual high-volume receiver. While the basic five-digit zip code is sufficient for most purposes, ZIP+4 codes help the USPS sort and deliver mail more efficiently.

Types of Zip Codes

There are several types of zip codes in the US system. Standard zip codes are the most common and cover a geographic area served by a local post office. PO Box zip codes are assigned to clusters of PO boxes at a specific facility. Unique zip codes are assigned to a single organization or building that receives a very high volume of mail, such as the IRS or a major corporation. Military zip codes serve Army Post Offices (APO) and Fleet Post Offices (FPO) for armed forces mail.