The Nuclear Regulatory Commission requires states to consider including potassium iodide as a protective measure in the unlikely event of a major release of radioactivity from a nuclear power plant. We evaluated emergency preparedness knowledge, including proper potassium iodide use, among the general public and emergency responders located around New Jersey's nuclear power plants. We found that knowledge about responder chain of command, evacuation routes, and some aspects of potassium iodide usage was incomplete among the general public and emergency responders.