https://ibb.co/cF4GTqZ it looks like this.

He has just been home and sleeping/playing since his morning walk, and this was not there on his morning walk. He doesn't seem to be in pain, his energy levels are the same as ever, and it doesn't really seem to hurt him when I touch the swelling either. He doesn't like it, and he shies away when I try to touch it too much, but he doesn't whimper or squeal or anything.

He's a 4 year old 9lb Chihuahua mix. We live in Ohio so I don't think it's a tick, since those die during the winter. Should I be worried about this? Or should we just keep an eye on it and see what happens in the next few days?

Thanks everyone! This is weird AF. Never seen anything like that before.