I started assembling some maps to chart among which peoples/in what regions different kinds of monstergirl-likes (that is, animal-human hybrids and other humanoids) are featured in mythology and folklore, but ran out of steam for now, so I'll post what I have.
I limited it to lore that implies or supposes that there is a group---or a whole species—of the creature in question (even if it's a small group, like the three Gorgons), while I ignored instances where a single individual deity or mythological figure might assume that form, but nothing else does.
I also only highlighted areas in which there is some unique-enough variant or derivative of a creature, which is why Italy often shows up blank---the Romans usually just adopted Greek mythology wholesale.
I've been using nothing but Wikipedia so far, and I find it somewhat wanting. I don't believe that Central Asia is this mythologically barren, and China ought to have more random shit as well, but on the pages and categories I searched, I couldn't find anything. I would appreciate if someone could link some good sources to use for further research.
How about we use this thread to assemble links and sources regarding monstergirl-like beings in mythology---your local/ancestral ones, or just ones that you know?
Interestingly, most centaurs or horse-people seem to be male-only.