>>56234298going off of bulbapedo, Kalos is also the highest populated region in general.
Using the highest population they've had:
Paldea (unrecorded?) might possibly be the largest since Mesagoza has a bunch of people (bulba says 669 just in there but might not be accurate)
Kalos (1288)
Alola (1005)
Unova (949) weirdly no change from bw to b2w2 also not including the potentially infinite wandering Castelians
Sinnoh (755) smaller in dp and bdsp
Galar (727) probably includes dlc locations since their populations aren't stated themselves (maybe the population counting autist died in 2020?)
Hoenn (694) smaller in rse
Johto (452)
Kanto (391) smaller in hgss and gsc
Sevii (212)
Orre (113) not a main series region but unlike the others has a recorded population
Hisui (111) technically sinnoh, but putting here cause centuries between the same place is basically a different region
Blueberry Academy (?) I'm still not sure if it's part of the Unova region itself or not. No recorded amount but maybe around here?
Kitakami (?) unclear if it's it's own region and population isn't recorded, but this feels right
Ultra Space (?) there's maybe less people you can interact with (including the trainers in Ultra Forest and hazmat guy in Ultra Ruin) but there could be thousands of people inside the Ultra Megalopolis buildings so i'm not sure
