United States Zip Code Overview

ZIP codes are a system of postal codes used by the United States Postal Service (USPS) since 1963. Before 1963, cities simply had postal zones” in 124 of the nation's most populated areas But when mail started to boom, in order to meet the growing demand, the U.S. Postal Service decided to add five numbers to addresses to make mail more efficient as a part of a Zone Improvement Plan (the ZIP in ZIP code stands for Zone Improvement Plan). ZIP codes are used by the US Postal Service to map the most efficient routes for mail carriers to follow.

ZIP Codes are numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a region in that group (or perhaps a large city) and the fourth and fifth digits representing a group of delivery addresses within that region. The fourth and fifth digits were proposed by Henry Bentley Hahn Sir which gives a more precise locale within the SCF 6 The SCF sorts mail to all post offices with those first three digits in their ZIP Codes. Robert Moon is considered the father of the ZIP Code. He submitted his proposal in 1944 while working as a postal inspector 5 The post office only credits Moon with the first three digits of the ZIP Code, which describe the sectional center facility (SCF) or "sec center." An SCF is a central mail processing facility with those three digits.