This is the Ebony Jewelwing....a species of damselfly. They hang out near streams and rivers. This one is from Cedar Bog, in Champaign County, yesterday.
They are metallic green, but can appear blue in some light. The wings of the male look all black in most light, but if you are lucky enough to see them in a shaft of sunlight you can see why they have the name "Jewelwing."