What is USA ZIP Postal Code?

USA ZIP codes are the postal codes which re-used to route mail more efficiently across the United States. ZIP in the postal code stands for Zone Improvement Plan. The first postal code was introduced in the year 1963. It was a 5-digit code why later extended up to 9-digits.

Types of ZIP Postal codes

There are four types of ZIP, Postal Codes in United States Database that are used -

Unique/single high volume address

PO Box


Standard (all other ZIP codes)

How are these ZIP codes assigned?

One thing worth mentioning here is that some ZIP codes span multiple states in the US. In general, the first digit of the code represents a group of states in the US. The first 3 digits determine Sec Center (the central mail processing facility) used to process and sort the mail. Mails with the postal code having same 3 digits are delivered to the same sec centers. And, that’s where they are sorted, where based on their last 2 digits they are distributed to local post offices.

ZIP codes for States, Counties and Cities

ZIP codes don’t cross state lines, but if it is efficient for a mail carrier to deliver the mail across the state line then they can.The edges of the boundaries overlap and hence when you are trying to assign ZIP code to a specific country it can get quite complicated.

You can go through the list of United States ZIP Code and lookup for the codes that you want.