Originally Posted by
Jagboi
If you exit the US by a land border (eg to Canada) how is anything recorded? There is nothing at the border, just drive out of the US to Canadian immigration.
Indeed, there is no check there. You can legitimately walk over the border at several points, notably Niagara Falls. You can still hand in the paper slips if you have them before departure, and you can download them online too. Canada, however, should stamp your passport at the main crossing points and that's OK for this purpose. There used to be a mini industry where people could mail in their departure slips but now they have given up on that reconciliation and just ask passengers to prove departure if the next visit is out of sync. If you make a new entry to the USA within the time of the previous time allowed then the system just clears it down automatically, so that should not need proof.
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Special tip: Anyone Global Entry and not USA/Canadian is advised to get their passport stamped on initial arrival into the USA, otherwise if you subsequently come back into the USA from Canada the whole thing looks a mess. So for example you visit NYC or Buffalo, you go over the bridge at Niagara Falls, have some Tim Hortons, come back to Buffalo / NYC. When you arrive back in the USA the port agents there cannot see your initial GE entrance to the USA (different system, GE and ESTA isn't for land borders) but they can see your Canada stamp. So ask for a stamp when you get to the USA first time around and explain you are leaving by a land border. When you come back into the USA the previous and still valid stamp removes any issues.