There’s a Google ad around here that says tri-state area. Where is that?
New Jersey, New York, and Connecticut, within commuting distance of Manhattan.
(or what Doug’s link says!)
Yes, it’s a very common expression around NYC. The Combined Statistical Area centered on Manhattan has a population of around 22 million.
The piper in the Google ad in question lives in Flushing, Queens. Home of the Trylon and Perisphere! (well, formerly …)
We try to keep it a secret but I guess it’s out.

And another one, just below that one.
And another just below that one too. Who knew?
We call Cincinnati the “tri -state” area because there are so many that work in it, but live in Indiana or Kentucky.
I’m betting just about any place that borders on several states gets called this.
Utah, Colorado, New Mexico. Or Colorado, New Mexico, Arizona. Or New Mexico, Arizona, Utah. Used to be called four corners but someone messed up the survey and they had to move the boundaries
Walden still has a valid question. Wiki lists four tri-state areas for Oklahoma:
1: with Missouri and Arkansas
2: with Texas and Arkansas.
3: with New Mexico and Texas
4: with Kansas and Missouri.
You would have thought that, with a bit of effort, they could have added (with) Colorado and New Mexico, as well as (with) Kansas and Colorado not to mention (with) Kansas and Arkansas. These people have no imagination!
I reckon it depends on which direction you’re facing at the time.
I have recently heard, at least twice, Virginia-Maryland-Washington DC, called the tri-state area. I know that some states (such as Virginia) are technically commonwealths, but they’re states in all but name. Washington isn’t. I’ve only heard this called the tri-state area within the last week or two. I hope it doesn’t catch on.
One and four are always combined, as far as I know, and called Four-States. There’s also the area called Five-States in the western end of the Panhandle: New Mexico, Colorado, Kansas, Oklahoma, and Texas.
The northwesterners are clearly underrepresented here.
To me, the “tri-state area” is eastern Washington (the state, not DC), northern Idaho, and western Montana. When I was a child, we often shopped at a store called “Tri-State” in Moscow, Idaho.
In the UK it would be a case of “perm any three from four”.
If you’re in the Islands, though, I think it’s “The Islands”, Scotland and Norway.
When I was growing up in Spokane, we called that “The Inland Empire.”
Redwolf