Collins–Valentine line

[3]The Treaty of Paris of 1783, which established peace between Britain and the United States, said the boundary was to be the 45th parallel, and it was generally assumed that that is where the line marked by monuments is.

Joseph Bouchette, writing about the re-survey agreed upon in the Treaty of Ghent, states that:In determining the geographical boundary between St. Regis and the Connecticut River, it was soon discovered that the original demarcation of the 45th parallel of north latitude widely deviated from the true course of that parallel, the position of which was carefully ascertained by the joint observations of the British and American astronomers employed on that service in 1818.

It was found that the pre-existing line was drawn almost wholly north of the true geographical bearing of that circle of latitude . . .

[4] The Webster–Ashburton Treaty of 1842 said that the measurement errors stand, so the boundary is where Collins and Valentine erected the monuments.

Most notable among these is the Haskell Free Library and Opera House in Rock Island (now part of Stanstead, Quebec, and Derby Line, Vermont, respectively.