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ZIP Codes: A History

Since 1963, mail has been zipping along its route thanks to the introduction of ZIP codes. But it hasn’t always been that way. Let's see how ZIP codes started and how they've changed over the years.

The prehistory of the ZIP code

In the early days of the U.S. Postal Service, mailing addresses weren’t regulated. You might have used the recipient’s street address along with the city and state, but you wouldn’t have seen a ZIP code. Mail was hand-sorted, and delivery relied on local knowledge of its intended destination. It was better than colonial days when people relied on friends and merchants to deliver messages, but not much.

Postal districts are formed

Use of the postal system increased significantly after 1940, so efforts were made to simplify the sorting and delivery process. In 1943, a system of postal districts was formed for major cities. Each district was assigned a one- or two-digit code that senders would place in between the city name and the state name. This helped, but the increased volume of mail soon created a need for mechanization.

The ZIP code is born

In 1961, the USPS increased efficiency by implementing the Nationwide Improved Mail Service system. NIMS standardized the physical dimensions for envelopes and shape limitations for packages, which made mechanization possible. Next, Postmaster General Edward Day took Philadelphia Postal Inspector Robert Moon’s proposal for improvements in the postal district codes and initiated the Zone Improvement Plan or ZIP codes. This plan expanded the two-digit city coding system into a five-digit system that included three digits for the general geographical area followed by the two-digit city district code. When addressing mail, you would now place the ZIP code at the end of the address, after the state.

Mr. ZIP takes the campaign national

Learning from the hardships of the telephone companies, which met widespread hesitancy when introducing area codes, Day launched a public pre introduction campaign. The cartoon character Mr. ZIP symbolized the speedy service and increased accuracy that the new ZIP codes would bring. Mr. ZIP worked, increasing acceptance of the idea to 90 percent and public use to 83 percent by 1969.

Today’s 9-digit ZIP code

In 1983, the USPS expanded ZIP codes further by introducing the ZIP+4 system. This nine-digit system added four numbers to everyone's ZIP code, identifying the side of the street for an address or, in the case of some very large buildings, the part of the building where the addressee is located. This allows more detailed sorting, so postal carriers can get your mail to you more quickly.

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