I think it's either yellow foxtail or green foxtail, there's also other foxtails.
This one grows at the edge of the garden by the alley; it's also a pest weed on crop (soybeans, corn) borders in central Il.

Several representatives of the
Pheleum - https://www.google.cz/search?q...
https://www.google.cz/search?q...
Timothy (Phleum pratense)
Alopecurus - https://www.google.cz/search?q...

Setaria - https://www.google.cz/search?q...


Polypogon - https://www.google.cz/search?q...

Pennisetum - https://www.google.cz/search?q...

It looks similar to the Yellow Foxtail, Setaria pumila, found in Hawai'i.

http://plants.usda.gov/core/pr...

http://weedid.missouri.edu/wee...

http://turfid.ncsu.edu/csPaged...

My first thought was Green Foxtail but I don't know why. http://www.illinoiswildflowers... but the yellow is also a possibility:
http://wwx.inhs.illinois.edu/c...
http://www.illinoiswildflowers...

According to my grass weeds book, it looks most like either yellow or green foxtail. Both have reddish bases to the sheaths, which it looks like it has from the picture. The easiest difference I can see in the characteristics list is that the bristles are yellowish to orangey in the yellow foxtail, and green, sometimes whitish or purple in the green foxtail. Other differentiating features are ones I can't see from the image.

Yellow foxtail has long hairs at the base of the leaf blades like this pic from IPM University of Missouri:

http://ipm.missouri.edu/IPCM/2...

There's more info on the page the above pic is from:
http://ipm.missouri.edu/IPCM/2...

The bristles don't look yellowish-orangey as far as I can tell from the picture so probably green foxtail on that basis?

I think I'll go w/ the green foxtail.
Thanks for all the input.