Prune in late March/early April. Don't prune in the fall.
Knock Outs are easy to prune with a pair of hedge trimmers. You can remove as much or a little as you wish while shaping the bush. Then go back with your pruners and remove any dead or damaged canes you may have missed.
I deadhead my knock Outs through out the growing season with hedge trimmers. It's fast and easy and keeps the bush shaped well.

Thank you so much!! I will prune them back in a couple of weeks. They seem to be coming to life already, so I don't want to wait too long!

Don't get in a hurry as a freeze can kill new growth. Early pruning can initiate new growth. We always seem to get a severe freeze in late March /early April followed by a flurry of questions here on how to salvage severely damaged growth. All this can be avoided by waiting until a more normal pruning time.
What's coming to life is more your body wanting to get outdoors into the garden. Pushing spring doesn't do the roses any good. It just causes more work and worry later.
I realize you're three weeks ahead of me which would make your pruning time the latter part of March. It doesn't hurt your roses to cut off new growth when you prune. I find it makes locating the proper place to cut a bit easier. Although I could prune now also as my bushes are beginning to show signs of coming to life, I'll wait until closer to mid April, my regular pruning time.
Right now, relax! Be Patient! Build something, take a little trip, read some books, do your spring cleaning. If you must go outside, clean up the beds, fertilize the lawn, or roam the garden centers. If you can work the soil, transplant any roses you have been wanting to get done. If bare roots are available, plant them now, hilling them up to protect the canes. Don't prune yet in your area. The American Rose center gardens were just pruned in Shreveport, LA in mid February and they're several hundred miles south of you.
They say spring moves north about 100 miles each week. Southern Illinois is about 500 miles north of Shreveport, so your pruning time would be late March. If you have to cut off a few leaves it won't hurt anything.

Karl always has good advice! All I can add is that when you do prune this spring, be ruthless. Knockouts aren't fussy so just whack away. I find they come back better, fuller and with even more blooms the deeper I prune them.

One other thing.
You can prune Knock Outs using a pair of hedge trimmers, cutting off as much as you want while shaping the bush. You don't have to go by an outword facing three leaflet bush as you might with other types of roses, unless you have to remove quite a bit of a cane.