I found several Mourning Cloak (Nymphalis antiopa) caterpillars and chrysalises on a small restroom strcuture in Mason park these last few days. This one is just getting started:
I’m not sure how long it takes one to spin a cocoon. This caterpillar and another were in exactly the same positions 18 hours later.
Here’s the finished cocoon from one who got started a little earlier. If it had been on a tree instead of a brick building I would have walked right past it without giving it a second look: