Southern Florida has several cities like this. A few have been somewhat successful:
https://www.google.com/maps/@26.9825804,-82.1857099,31160m/d... https://www.google.com/maps/@26.6300975,-81.9789861,24756m/d...
Others, not so much:
https://www.google.com/maps/@26.6204017,-81.6442622,17018m/d...
There's also this curious region which started as a land scam but ended up becoming a somewhat lawless area now ruled by a hunting club:
https://www.google.com/maps/@27.7771326,-81.3102668,7540m/da...
The place is dangerous and violent but remote, and authorities keep their distance. It feels strange to think that a place like this exists an hours drive from Disney World.