I'm in Illinos, and just started looking into this. I guess the Illinois Department of Agriculture issues an applicators license, which you go through the University of Illinois for. Sounds like a pain, but hubby and I are going to sign up!
I also just signed up for my Certified Arborist workshop. When hubby took it a couple years ago, I helped him study so much I could have passed the test to, and he's been on me ever since!