A worldwide community photographing and learning about wildlife
Lotus corniculatus
I presume this is plant native to the area originally, but it could just as easily be something non-native.
In a nature preserve in the Chicago suburbs, in an area being restored to be closer to the native prairie it once was.
Could be yellow wild indigo or pencil flower, both of which sometimes have small clusters of flowers like this. There are others, too, that don't immediately spring to mind. I doubt it can be ID'd without a look at the leaves.