http://www.teamsteverhyner.com/the-story-of-the-fourth-of-july/#more-358

It wasn't until 100 years after the Declaration of Independence that the 4th of July was declared a national holiday along with Christmas by an act of Congress. July 2, 1776 was the day the Continental Congress approved the Declaration not the day it was signed. It was actually signed on August 2, 1776.