Good Question: What Are The Numbers In The ZIP Code?

MINNEAPOLIS (WCCO) -- They are the five numbers that stand for home. Since 1963, ZIP codes have been a part of just about every piece of mail that travels through our system. But what do those numbers stand for?

"There is a code, and we're about to crack it," said Pete Nowacki, spokesman for the U.S. Postal Service in Minnesota.

Across the country, there are more than 42,000 different ZIP codes in use.

"Generally you can take the first number and that will line up with the state," said Nowacki.

Every ZIP code in Minnesota and Wisconsin starts with a 5. So do ZIP codes in Iowa, Montana, North and South Dakota. The numbering system starts in the east and moves west, so the 0's are in Maine, Connecticut, and Vermont, the 1's are Delaware, New York and Pennsylvania, all the way to ZIPs starting with 9 in Alaska, Hawaii and California.

The first three digits of a ZIP code are linked to a sectional center facility. There are 455 of them across the country; many facilities (including the Minneapolis facility) handle a couple of different codes.

But what, exactly is a sectional center facility?

"It's really representative of the mail processing center where the mail for that area is sorted," said Nowacki.

"The next two numbers are going to designate your specific delivery post office," said Nowacki.

So for example, Waseca's ZIP code of 56093 breaks down like this:

"The 560 means the Mankato distribution center, the 93 means specifically Waseca," Nowacki explained.

After the 5-digit ZIP code gets the mail to your local post office, the "plus 4" code gets it to your neighborhood.

"Do you have to write it on your letters?" asked WCCO reporter Jason DeRusha.

"No, of course not. Our machinery reads the address, then sprays a bar code that corresponds to that 9-digit number," said Nowacki.

The first two digits of the "plus 4" code sort the mail to a sector segment.

"It just breaks the mail down finer and allows the machinery to sort the mail closer to where it's ultimately delivered," said Nowacki.

The last two almost gets your letter to your specific house.

"It might be a chunk of 6 to 8 houses," said Nowacki.

If your mail is delivered to a mailbox at your house, you probably have a different "plus 4" code on your side of the block than your neighbors across the street, because the point of the code is to automate the sorting for the letter carriers.

"Then there's the secret last two numbers," said Nowacki.

Rarely written down but always encoded into the bar code, the last two numbers make the whole number unique.

"They zero it down right to your house," said Nowacki.