Imma guess, like most things it seems, they always have been, we just see it more thanks to the internet.

This is an interesting point and makes me wonder: are there historical accounts of furries in history? I guess you could count things like werewolf stories, maybe, but that seems like a stretch…? I get the feeling I’m describing an existing field of study and hope there’s something to read about it?

Lots, this kind of thing goes back deep into pre-history. I mentioned in another comment in this thread that the oldest known sculpture is of a furry and the oldest known cave painted art is furry art. Lots of gods and creatures of myth are human/animal hybrids of various sorts, or straight up animal spirits.