Have you taken a sample of this to your counties Cooperative Extension Service office?
Some location descriptor other than United States might also help.

Use this clickable map to locate your county's Extensive Service office:
http://www.csrees.usda.gov/Extension/

Here is a link that might be useful: locate your county's Extension Service office

Looks like one of the Persicarias.

Thank you all for the info

This is Acalypha virginica, commonly called threeseed mercury or Virginia copperleaf.