Length of the U.S.–Canada Border: World's Longest International Boundary

The land and water boundary between the United States and Canada spans 5,525 miles (8,891 kilometers), making it the longest international border in the world.

Breakdown

• Land border: ~5,061 miles (8,145 km)
• Water border (Great Lakes, rivers, straits): ~464 miles (747 km)
• Alaska–Canada (Yukon/BC) segment: 1,538 miles (2,475 km) — included above.

Key Features

• 8,000+ monuments/markers.
• Crosses 13 U.S. states (ME, NH, VT, NY, PA, OH, MI, MN, ND, MT, ID, WA, AK) and 8 Canadian provinces/territories (NB, QC, ON, MB, SK, AB, BC, YT).
• Peaceful, largely undefended; managed by International Boundary Commission (IBC).
• 20+ major land ports of entry; busiest: Detroit–Windsor (Ambassador Bridge/Tunnel), Buffalo–Niagara.

Historical Note

Defined by multiple treaties: 1783 (Paris), 1818 (Convention), 1842 (Webster–Ashburton), 1846 (Oregon Treaty), 1903 (Alaska Boundary Tribunal). Final demarcation completed 1930s.