Very similar to C. pennsylvanicus, but pronotum has wide dark band, instead of an irregular dark spot. Elytra of C. marginatus often more extensively dark than pennsylvanicus. C. marginatus is also somewhat smaller and is active earlier in summer than C. pennsylvanicus.
Old field habitats with flowers.
Not the best shot since it's just of the back but does anyone know what kind of bug this is? It's it a firefly? - UPDATE I found more pics of it, these were taken in a different location at a different time but I think it's the same beetle.