Partly in Vermont: A Borderline Case

"This is the border," says Irene Bolduc, stepping in off her porch and pointing to the edge of a doorframe. "See, over in the living room, you are in the United States. Step into the kitchen, et voilà, you are in Canada."

Here at the edge of northern Vermont, the international boundary lies right across a quiet but thickly settled small town. On the American side, the town is called Derby Line, Vt.; on the Canadian, Rock Island, Que. Local historians believe that the border runs the way it does because an 18th century...