Isles Phelipeaux and Pontchartrain

File:Mitchell Map-06full2.jpg

The Mitchell Map with the islands on Lake Superior in it.

Isle Phelipeaux (or Île Philippaux) and Isle Pontchartrain are phantom islands in Lake Superior, believed at one time to be real, shown on early maps, such as the Mitchell Map, of Lake Superior as located between the Keweenaw Peninsula and Isle Royale.

Although non-existent, Isle Phelipeaux was referenced in the 1783 Treaty of Paris that ended the American Revolutionary War. A portion of the boundary between the United States and British colonies in Canada was described as running "through Lake Superior northward of the Isles Royal and Phelipeaux to the Long Lake." It had first appeared on a map prepared by the cartographer Bellin in 1744. It continued to appear on maps of Lake Superior for many years, including the Mitchell map used in the Paris peace talks, in 1783.

During the 1820s, when surveys were attempting to determine the International Boundary from the Lake of the Woods to Lake Superior, it was discovered that Isle Phelipeaux did not exist; surveyors were also unable to determine what body of water was meant by the "Long Lake" referenced in the treaty.

See also

• Isle Royale Agreement
• Webster-Ashburton Treaty