What type of nut is this?

I live in Illinois and picked this nut up off the ground where I work. Nobody seems to know what kind it is. It is the color of a chestnut, but oblong. I didn't see any shells around it, like a walnut. Does anyone know what it is? Thanks

 

Could they be acorns?
Could you go back to where you found these and take some photos of the tree from whence they came---leaves, etc.?

 

Yep, most definitely acorns.

 

Native squirrels, as well.

 

these are definitely Acorns - have millions of them in Spain, and the cured ham from the pigs fed on them is out of this world!!

 

Acorns of an oak in the white oak group (Quercus sect. Quercus).