There will definitely be Lileep in the slowpoke well and caves since it was/is a rock type! But not in the bodies of water like the Ilex Forest, since it just seems to be a little pond. Since it attached itself to the sea floor a hundred million years ago (and who knows what that looks like).

That said, because it's found in the Slowpoke Well, it'll also spread over to the Ilex Forest anyways.