USA Zip Codes - 500 Most Populated Zip Codes

A postal zone was established for the first time in 1943 by the United States Postal Service Department. Thousands of experienced postal workers were forced to abandon their jobs to serve in the military during World War II. For this reason, the Post Office Department implemented a zoning address system in 124 cities, which allowed mail to be divided by personnel who did not have the same expertise and experience as those who did have it.

Using computers, accounts were centralized by 1963, and massive volumes of mail were sent in the form of bills, bank deposits, advertisements, and magazines; mortgage bills and payments; Social Security checks and other forms of mail were being sent at the same time. In order to keep up with the amount of mail, the Postal Service sought to improve its processes in order to be as efficient as possible. The outcome was the Zoning Improvement Plan (ZIP) Code, which went into effect on July 1, 1963, and is still in effect at the time.

ZIP codes are made up of five digits. From zero in the Northeast to nine in the West, the first number is given to a vast geographical region of The United States, with the first digit referring to the state of New York. In the next two numbers, you may find populous concentrations and sectional centers that are easily accessible through common transit systems. They are the last two digits of the code. They are used to identify small Post Office buildings or postal codes in bigger cities.

In the United States, there are roughly 42,000 zip codes as of the year 2000.