Yes, I agree this is a species of Bidens, of which there are 10 species in Illinois.

The Beggarticks Seedcropper/Cirrhophanus triangulifer(Goldenrod Stowaway Moth caterpillar) on pg 339 of Owlets was the only one of the images that closely resembled this caterpillar of mine. Wagner didn't give much description, so I hesitated about it being my caterpillar. The only description, besides the photo, that Wagner gives is in the intro to Seedcroppers on the same page. He says that these caterpillars have a short, scalelike spinneret and that SD1 on A9 is hairlike, and this is true of this caterpillar. I have other photos where this is possibly more obvious. I agree that this is the caterpillar. Isn't it fitting that the larvae would feed on a flower that the adults will later rest upon to camouflage themselves during the day? I have a better photo of the flowers I will add here to see if you can verify it is Bidens. I will have to go back to this field and search more now, since the irony is that we've been looking for our first Goldenrod Stowaway Moth on every yellow flower possible lately. Never expected to find the caterpillar. That's happened with a few other caterpillars/moths as well.