We got an important comment from the official AT.
UPDATE:
“Actually the terminii of the Appalachian Trail were determined by an act of the U.S. Congress when it established it as the first National Scenic Trail in 1968. To “lengthen†the official Trail would take a similar act of Congress.”
Martin A. Bartels – www.appalachiantrail.org
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original post:
Most finish the AT at Mount Katahdin, Maine.
But the Appalachian Mountains continue into Canada. Surely the standard 2,175mi is not long enough.
You could cross the U.S.-Canada border at Fort Fairfield and add another 500mi or so. This is one of the extensions referred to as the International Appalachian Trail.
Trek Through to the True End of the Appalachian Mountains – GORP
But is that far enough?
Why not extend your walk through to the north tip of Newfoundland?
source – InternationalAT.org
Walking for walking’s sake is not necessarily a good thing. Because it’s there, not a good enough reason.
Be discriminating when you choose your hikes. That’s what besthike.com is all about.
Life is short.
besthike.com 
This is a very interesting piece of information,
I used to think AT is from Maine to Georgia until one time I read in a magazine that it extends to Canada, and at that time I was wondering, “ouch I need a visa to cross the border.”
Actually the terminii of the Appalachian Trail were determined by an act of the U.S. Congress when it established it as the first National Scenic Trail in 1968. To “lengthen” the official Trail would take a similar act of Congress.
You can find out more at our Web site, http://www.appalachiantrail.org.
Excellent point!
We’ve updated the original post to include your comment prominently.
I’ve personally never hiked any section of the AT. But I plan to get out for Appalachian Trail Days, May 18-19-20 2007 in Damascus, Virginia. And get better educated about what the AT does for all hikers everywhere.
Thanks for your continued good work at appalachiantrail.org.