I believe it is Panicum capillare - witchgrass.

That works. Thanks Peren.

https://www.illinoiswildflowers.info/grasses/plants/witch_grass.htm

The link above has ways to distinguish witch grass from a couple of other similar panic grasses.

Nice link NHBabs. That Illinois Wildflowers site is the best one I've seen for consistently providing good photos, full plant descriptions, and quick ways to distinguish from similar plants. You have to drill down from their home page to get to the right species, and that part is sometimes confusing. I wish they had a page with all of their wildflowers listed together.

Jay, if I need a description, i.e. for Potentilla recta, I just search Google for "Illinois Wildflowers Potentilla recta" to get a quick link to that species. Once on the right page, you can hit the "return" link at the bottom to get to a page that lists the rest of the species in Illinois from a particular genus.