You might still find some cats
Here in central PA I'm still finding Black Swallowtail cats outside on my rue. We've only had two nights so far this fall in which it has gotten down to 32 degrees and those were just recently. Most years we have our first frost by Oct. 15, and we'd have had more freezing nights by now than just two.
The rue holds up pretty well in cold temps, but now that I have a few small cats (I also have some that should pupate soon), I brought some cuttings inside just in case and have them in a jar of water until I need more to feed the cats. Two of the cats I found today are barely 1/4" long, and the other one is about 1/2". I haven't counted how many BSTs I have here to release in the spring, but there's got to be at least 50.
This year was a great butterfly year, but wow, was it HOT this summer! I don't even think there was a lull here all spring and summer. I was still seeing butterflies here up until a few days ago. The latest ones I saw were Common Checkered Skippers and Silver-spotted Skippers. I imagine that people in the southern states are still seeing a fair number of butterflies then?
I saw an enormous amount of Eastern Tiger Swallowtails this year. I think those and Silver-spotted Skippers were my two most common butterflies. I saw Red Admirals for the first time in several years but didn't get any cats (the false nettle was barely hanging on with our temps and drought). I didn't see even one Giant Swallowtail here this year. It's interesting to see how things change from year to year.