What would happen to a US citizen who snuck into Mexico, and decided to stay a while? I could exist there indefinitely if I had access to an ATM. If I went off the beaten path, would I ever be challenged? And if they caught me, then what?
If you enter by land, Mexico allows U.S. citizens visa-free travel as long as you stay within a certain distance of the border, for up to 72 hours. Beyond that they have a form of tourist visa called a “Tourist Card”, that is issued as a matter of routine anytime you book most travel to Mexico outside of crossing by land. It will usually be included with any bookings to Mexican resorts and they are very frequently (but not always) included in your airfare for a $22 surcharge. If you have a tourist card, as an American, you can basically stay in Mexico forever. The rule is 180 days on that card, but they have no limitations on reissue or cap on how m any times, you do have to go out of the country and back in, but it’s common for people living in Mexico on a tourist card to do “border runs” where they dip back to the U.S. for a day or two, get a new tourist card and refresh their 180 days.
There’s people who even own homes in Mexico with no more than a tourist card, I’m not sure if that’s 100% legal or kosher, but it doesn’t seem to be tightly regulated.
For more permanent and non-transient immigration, Mexico has a pretty onerous immigration system with limited permanent / work visas available to Americans, kind of the same deal as Mexicans trying to legally immigrate to the United States.
AFAIK if Mexican police detain you and find you’re in country on an expired tourist card, they will absolutely deport you, same as America would do to a Mexican.