Here’s a ZIP code database. It has a “multiple county” flag that designates which ZIP codes are in multiple counties.
Unfortunately, only a sample is downloadable for free, but it does show an example of a ZIP code, 38583, that is spread across five counties.
I was hoping to find how many ZIP codes span multiple counties, but the free ZIP code databases I’ve been able to find in a cursory search don’t seem to include that information.
Actually, now I wonder about something. I always thought the city and state information on a piece of mail in the US was redundant (and, in most cases, it is – a letter will get to its destination just fine, generally, with only the address and ZIP on it), but now, I’m thinking that in the case of these localities with multiple ZIP codes, it actually is necessary.
Yes, that’s the point. Even postal addresses are for the convenience of the PO, and don’t necessarily have to represent the political boundaries within which you live. The address for your mail might say “ABC Town” when you don’t in fact live there, if the Post Office which handles your mail itself is in ABC Town.
If I’m understanding your question correctly, the answer is No. The ZIP code tells what post office handles the mail; that directs the mail to the specific building from which the delivery is made (where the carrier who delivers it to your letterbox picks it up, e.g.). That building need not be in the city or county or state in which your letterbox is located, but it’s still where your carrier picks it up. For example, mail destined for an address in the North Dakota part of ZIP code 59221 still goes to the Fairview, Montana, post office. Putting “North Dakota” on the envelope adds no additional helpful information; the rural carrier who drives the North Dakota part of the route starts his/her route at the Montana location and picks up the mail there.
If there are multiple ZIP codes for a town (Topeka, Kansas, for example has 66601, 66602, 66605, etc.), those may or may not correspond to a single delivery station, but the ZIP code will be enough to route it to the correct location. For example, in Topeka ZIP 66605 refers to the southeast section of the city, and all of those carrier routes work out of the Hi-Crest Station, whereas 66601, 66603, and 66612 addresses are all served from the main post office downtown. In each of these cases, the ZIP alone is enough to get it to the right post office for the carrier to collect it.
Oh, I was envisioning a ZIP code encompassing two cities, both with say, a Main Street. But I just reminded myself we’re talking about ZIP codes across counties. That said, it does appear there are ZIP codes that cover more than one town. If we’re just using the 5-digit code, would it not be possible for two towns to both have an address like 6 Main Street, or are ZIP codes laid out to avoid that?
Anyhow, getting back to this question, I found this from a 1994 census report that states:
Emphasis mine. A little outdated info, but gives us a rough idea.
ETA: And I’m wondering if I’m reading that correctly, because that would work out to something like 20% of all zip codes, no? (The number fluctuates, but there’s about 43,000 ZIP codes.)
Yes, the Post Office prevents that. And they have a lot of pressure to bring to bear on other involved local government bodies. Like the ultimate, refusing to deliver mail to ‘invalid’ addresses.
They work with local cities to avoid conflicting street names. They’ve even reminded cities when a name pronounced aloud or over the phone could be mis-heard as another local street name. When there are conflicting street names, they work to prevent overlapping address numbers (like if one city has 6 Main St, they try to ensure the other city in that zip with a Main St has 206 as the lowest number on that street.)
The Post Office has a whole lot of influence on the street names & address numbers used. Especially in new developments; older cities mostly can’t be changed & they just live with some ambiguities. And what the APost Office says goes: everybody from the utilitiy companies to voting registrars to Google Maps to every mail house use the Post Office database of valid delivery addresses to start from.
(It takes time for all these organizations to update their files from the PO database. I had friends who were one of the first to move into a new development. They had lots of minor problems when their address wasn’t listed as a ‘valid address’ on somebody’s computer system. Like when their friends tried to get to their new house, but the directions on their cell phones couldn’t find it. Ordering things online or by mail order often had their address rejected as ‘no such address’. One utility billing department refused to set up an account at that address, even though their installer had been out that day to make the connections. Too tired from moving to cook, they ordered pizza for them & their volunteer helpers – but they had to drive & pick it up; the delivery database wouldn’t accept their address.)
It’s certainly a reasonable question to ask, about identical addresses. One of my commutes, a mere 15 miles or so, crosses two different Elmwood streets (in two different but adjacent suburbs). And pretty much all cities around here number their north-south streets with the lake as the origin, and both streets are close enough to the lake that they’d probably have overlapping number ranges.
Very impressive! Thank you!
My old ZIP code, 21208, included parts of Baltimore City in what was a Baltimore County ZIP code. The good thing was that insurance rates were based on ZIP codes, so I paid county rates, even though I lived within the city line.
In the UK, two routes could, for example, cross at right angles going through the same area, because the code refered to the mail route, not to an area that it served.
That was not the original design of the US/Aus zip code systems.
An example of this is the house where I grew up, and where my mom still resides. New Hyde Park, NY, and Garden City Park, NY are both in the 11040 zip code in Nassau County(although a tiny bit spills into Queens County as shown on Colibri’s map). I lived on 2nd St., in GCP. There also were numbered streets in NHP. When they instituted zip codes, they renamed all of the streets in New Hyde Park as North X Street and South X Street, with Jericho Tpke as the dividing line. So now, if you type XX 2nd St, Garden City Park NY, or XX 2nd St, New Hyde Park NY into Google maps, it will take you to the same location, since there is only one 2nd St. in 11040.
I just double-checked the two Elmwood Roads I mentioned on Google Maps. It looks like one of them has addresses from roughly 400 to 1400, while the other is roughly 250 to 600, so there would be some overlap. But they are in different zip codes.