The United States forms Canada's southern border. This boundary, the world's longest undefended international land border, stretches over 5,500 miles.

Border Details

Canada shares its entire southern land boundary exclusively with the United States, spanning eight Canadian provinces and 13 U.S. states. The border follows the 49th parallel north for much of its length, with notable exceptions like the Great Lakes and rivers. Established through treaties post- American independence, it runs from the Pacific Ocean to the Atlantic.

Key Provinces and States

  • British Columbia : Borders Alaska, Washington, Idaho, Montana.
  • Alberta, Saskatchewan, Manitoba : Align with Montana, North Dakota, Minnesota.
  • Ontario, Quebec : Touch multiple states via lakes and rivers, including New York and Michigan.
  • New Brunswick : Shares with Maine.

Fun Geography Tidbits

Forum chatter highlights quirks, like remote areas where crossing feels seamless—think accidental detours into Canada for candy. Others joke about perspectives flipping "south of the border" in Alaska contexts. No other sovereign country claims this southern spot; maritime edges touch Denmark's Greenland and France's Saint Pierre and Miquelon, but land is purely U.S.

Recent Context

As of January 2026, no changes affect this border amid U.S. President Trump's reelection focus on security talks. Discussions on Reddit geography subs confirm the basics endure.

TL;DR: United States, full stop—longest friendly line on Earth. Information gathered from public forums or data available on the internet and portrayed here.