Very nice! A spicebush swallowtail. Spicebush and Sassafrass are their host plant.
-Elisabeth

That one in particular is a male. Females have blue at the back and males have a dusty green color.

"Caterpillar hosts: Spicebush (Lindera benzoin), sassafras trees (Sassafras albidum); perhaps prickly ash (Zanthoxylum americanum), tulip tree (Liriodendron tulipifera), sweetbay (Magnolia virginiana), camphor (Cinnamomum camphora), and redbay (Persea borbonia)."

Here is a link that might be useful: Spicebush Swallowtails

Thank you both so much for the ID. I guess I never thought to check Spicebush Swallowtail because I do not have any of the host plants it uses, nor have I seen these plants in the neighborhood.