While on a hike through a nature preserve here in central IL, we came upon this pretty purplish/blue flower. After looking through a few wildflower books, we couldn't really come up with a definitive ID, though we were thinking something in the Skullcap family. Can anyone help?

Sorry, I just noticed we didn't get a picture of the leaves, but as I recall they were similar to a salvia leaf and there was just this one flower stalk coming up from the plant, which was about 2" tall.