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TANEY COUNTY, Mo. – Why is there one zip code in Missouri that starts with a 7 instead of a 6? Is there a ghost town there? Well, the answer was a mystery to us until the U.S. Postal Service called.

A Reddit thread titled The Curious Case of Lead Hill, Missouri was posted in November. The author asked why, “A town in Missouri, with no population, with no map to define the geographic area in Missouri’s Ozark Timeshare Trap seems a little sus.”

Dozens of amateur sleuths chimed in with guesses, but there is an answer.

The meaning behind the numbers in zipcodes

First a history lesson. Until the invention and national implementation of the zip code in 1963, the U.S. Postal Service sorted all mail by hand. The growing population and continued drive into the west necessitated a more efficient way of handling the mail.

The Untold Story of the Zip Code:

A nationwide standardized coding system for mail would increase processing efficiency. Consider just a few examples. A code could resolve problems associated with nonspecific references such as multiple cities in the United States with the same name. A code could also allow further mail grouping for easier distribution, logistics handling, and transportation routing. For example, the code would increase cross country shipping densities while allowing mail to be sorted into smaller groups than the city level. Lastly, a code is easier for computerized equipment to recognize than addresses.

USPS, April 2013

Ultimately, the USPS divided the country into 9 zip code zones, in which the first number corresponds to a specific zone. Both Missouri and Illinois are in Zone 6. Therefore, the zip codes in each state all start with the number six.

Or at least they’re supposed to.

Enter zip code 72643.

Zip-Codes.com identifies code 72643 as Lead Hill, Missouri, located in the 417 area code. It says the zip code receives standard mail delivery but there are not many people who live there, making it seem as though Lead Hill is a ghost town. Oddly enough, there is a Lead Hill Township about 40 miles north of the Missouri-Arkansas border that has about 174 residents, which can possibly confuse some people trying to research the topic.

What does the U.S. Postal Service have to say about it? It identifies 72643 as Lead Hill, Missouri.

Mark Inglett, a spokesman for the USPS, says that there are three homes in Missouri located along Horseshoe Bend Road on an Arkansas peninsula that crosses the state line. This is why the zip code starts with a 7 instead of a 6.

The postmaster in Lead Hill, Arkansas, is responsible for delivering mail to the 72644 zip code as well as those three customers on the nearby peninsula.

But why? Inglett says it’s more efficient for mail carriers in Lead Hill, Arkansas to drive there than it would be for postal workers in Missouri to cross Bull Shoals Lake for three customers.

As it turns out, this bleeding over of zip codes occurs about 20 miles east, where the 65761 zip code (serviced by Theodosia, Missouri) crosses the state line into Arkansas. And if you look to the northeast and northwest borders of Missouri, there are two Iowa zip codes—51640 and 52626—that have bled into the state.

Ghost towns? No. Just mail carriers trying to figure out the best way to get letters and packages to their intended recipients.