The most likely place I can think of is RoI/UK, but could be somewhere else, just curious it there is any private residence in the world where one side is in country X and the other in country Y? due to the ease of travel between N and S Ireland that would be my guess, if anywhere, there were such a thing.
I would imagine the Belgium Netherlands border is rife with examples, particularly the town of Baarle-Hertog/Barle-Nassau.
EDIT: From wiki: “Some houses in the town of Baarle-Hertog/Baarle-Nassau are divided between the two countries. At one time, according to Dutch laws restaurants had to close earlier. For some restaurants on the border, this simply meant that the customers had to move to a table on the Belgian side.”
Yes, many of them. This happens most famously in the US along the Vermont and Quebec border, specifically Upper Derby, VT and Stanstead, QC. Here’s one that the front door is on the American side, but the door on the right side is Canadian. The house is the grey stone one if it doesn’t center it right for you. There’s a little white post in the front yard to the right of the door that marks the border and it basically bisects the house.
Another bit about Baarle is that for houses on the border, the owner pays taxes in the country where their front door is. Most such houses have two front doors, one in each country. They board up the door in the country with the higher taxes, but are ready to switch doors if the tax rates change.
It also has the only library in world that operates in two countries. The library isn’t much bigger than a large house and used to have free access to both countries with few rules until 911 and still does to some degree as long as people follow the rules but residents of the U.S. and Canada can use it just by walking in their own door. Once inside, it doesn’t matter what side they are on until they leave.
Estcourt Station, Quebec/Maine has some homes that fall on the border like that.
And to expand a bit beyond this thread, that library has been in thenews recently as a place for people to meet their families that are banned from entering the respective countries due to immigration problems. Very interesting, but it really shows how arbitrary laws and borders can be!
If you call Texas “A Whole Nother Country” 
State Line Avenue, Texarkana, Texas and Texarkana, Arkansas!
The Quebec town is Derby Line. There is a township called Upper Darby a suburb just west of Philadelphia where I lived for some years.
Yep. I live close to there. Not sure if any houses actually sit on the stateline. Our property is in 2 counties. I could spit out my back door into the next county.
No houses are actually on the state line right around Texarkana, but one of my high school buddies lived on South State Line Avenue. His house was in Arkansas, but his (rural-style) mailbox was in Texas.
Hey, that’s wild, like in the Twilight zone, step out the door, from one dimension to another. 
They think of everything:
There’s a house nearby which has the front door and garage door in different counties.
Wow, really? That’s pretty hilarious actually.
“Which door are we using this year, honey?”
Things sound not as fun if you live on the wrong border. Good luck trying to get someone to fix your water or electricity, or your mail delivered, if you live on the wrong side of the street.
German Post office and Dutch Post Office
Correction: The Eurode Business center, a business building that straddles Germany and Holland, but where letter posted takes a week to go to the other side.
The wiki page on Hotel Arbez lists most examples already mentioned including the Kalin Restaurant, the Haskell Opera and Free Library
and Barle Nassau/Barle Hertog
with restaurants that shift patrons based on closing timing regulations
Farms and business taxed on the front door
https://www.citylab.com/equity/2012/02/most-complicated-border-town-world/1267/
http://nowiknow.com/scrambled-city/
The crooked bank that needed 2 country joint investigation force etc