Ever wonder why we have Zip Codes and what they mean?

Life Before ZIP

In 1943, the US was in the thick of WW2 and many our postal workers had gone into the service. The inexperienced postal clerks that stepped in to fill their shoes had trouble sorting the mail. To make things easier, postal zones were introduced that broken major cities into numbered districts. Addresses now included their one or two digit zone numbers after the city name, for example: Chicago 14. 

Zone Improvement Plan

In 1963, five-digit ZIP Codes as we know them were introduced. The ZIP stood for “Zone Improvement Plan.” The Post Office also standardized the two-letter state abbreviations at this time. Prior to this, the abbreviations had ranged from two to five letters. For instance, California was written Calif. The postal service decided to shorten the states to two letters because it left more room for the 5 digit zips, since most addressing systems had a maximum 23-character line.

The ZIP system was invited by postal inspector Robert Moon, who first submitted his idea in 1944. His proposal introduced a three digit code which described the sectional center facility (SCF) or central processing location where mail was sorted in each region before being sent to local post offices. Incidentally, the first digit of the SCF code (and therefore the ZIP code) represents the state or territory, as follows:

  • 0 = Connecticut (CT), Massachusetts (MA), Maine (ME), New Hampshire (NH), New Jersey (NJ), New York (NY, Fishers Island only), Puerto Rico (PR), Rhode Island (RI), Vermont (VT), Virgin Islands (VI)
  • 1 = Delaware (DE), New York (NY), Pennsylvania (PA)
  • 2 = District of Columbia (DC), Maryland (MD), North Carolina (NC), South Carolina (SC), Virginia (VA), West Virginia (WV)
  • 3 = Alabama (AL), Florida (FL), Georgia (GA), Mississippi (MS), Tennessee (TN)
  • 4 = Indiana (IN), Kentucky (KY), Michigan (MI), Ohio (OH)
  • 5 = Iowa (IA), Minnesota (MN), Montana (MT), North Dakota (ND), South Dakota (SD), Wisconsin (WI)
  • 6 = Illinois (IL), Kansas (KS), Missouri (MO), Nebraska (NE)
  • 7 = Arkansas (AR), Louisiana (LA), Oklahoma (OK), Texas (TX)
  • 8 = Arizona (AZ), Colorado (CO), Idaho (ID), New Mexico (NM), Nevada (NV), Utah (UT), Wyoming (WY)
  • 9 = Alaska (AK), American Samoa (AS), California (CA), Guam (GU), Hawaii (HI), Marshall Islands (MH), Federated States of Micronesia (FM), Northern Mariana Islands (MP), Oregon (OR), Palau (PW), Washington (WA)


Once the mail is sorted overnight at the SCF, it is sent to the appropriate local postal center for morning delivery. The final two digits of the ZIP code were later introduced to denote these local centers. These codes don’t always follow geographic logic. Rather, they follow mail delivery routes. A densely popular urban area may contain many different delivery centers, whereas six outlying counties could be served by a single mail route.


ZIP Codes would be useless unless the general public caught on to using them. The postal service introduced a cartoon character called Mr. ZIP to promote the use of this new fangled system. The character was actually designed by Harold Wilcox, whose father was a postman. Mr. Wilcox’s advertising agency, Cunningham & Walsh, made the image for Chase Manhattan Bank for use in a bank-by-mail campaign.


Postal carriers handed out cards featuring Mr. ZIP to their route households. He also appeared on the edges and lickable parts of stamp sheets, reminding people to USE ZIP CODE. Because it was the sixties, Mr. ZIP was soon merchandized, appearing on games, toys, lunch boxes and buttons. The postal service even contracted “The Swingin’ Six” to write a catchy tune about ZIP codes. Incidentally, it was these early ad campaigns that launched the enduring term snail mail.


ZIP +4

In 1983, the U.S. Postal Service introduced an expanded ZIP Code system that it called ZIP+4. The four additional digits identified a segment within the five-digit delivery area. This could denote a city block, apartment group, or even a single address that received mail in high-volume.  However, without a friendly cartoon character at its helm, the notion of a 9 digit ZIP met public resistance. Instead, the people of the Eighties did what people of the Eighties did best: invent a machine to figure it out for them.

Now-a-days, mail is read by a multiline optical character reader (MLOCR) that can actually read a handwritten address and from it, determines the correct ZIP+4 Code and specific delivery point (which gets 2 additional code numbers). The machine then sprays a barcode that contains all 11 digits onto the face of the envelope. Other machines then read this barcode and sort the mail further, all the way down to the specific route of the mail carrier.


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