There is a street in Derby Line (VT)/Rock Island, (QC) where the border runs down the middle of the street, so your neighbours across the street, are in another country.
After 9/11, apparently, neighbours on one side of this street were required to drive to Customs, up to a mile away, register, and then drive back to their neighbour’s house. While they were supposed to do thus before 9/11, I don’t believe that it was enforced; now it is, and apparently, vigourously. Borrowing a cup of sugar could become arduous, as well as an international incident!
Yup,I've driven down that street before...it's called Canusa Street,as in "Can" (Canada) "usa" (USA).My understanding is that the entire street itself is in Canada but there's a short stretch where the houses and driveways on one side (the south side) are in the US and,as a result,the mere act of leaving your driveway/front yard means you've entered Canada.While there,visiting the Haskell Library (which I had heard of) the area was crawling with US Border patrol cars.Didn't see any Canadian border patrol people except for the ones at the small entry station down the street.
From what little I've read those towns,historically,always pretty much behaved as one...border officials of both countries kind of waved you through,or looked the other way,when you crossed the border in either direction.But after 9/11 things changed...largely,if not entirely,because of the US Border Patrol.