Via Time Magazine:
#1 Independence Was Declared on the Fourth of July.
America’s independence was actually declared by the Continental Congress on July 2, 1776. The night of the second the Pennsylvania Evening Post published the statement:”This day the Continental Congress declared the United Colonies Free and Independent States.”
So what happened on the Glorious Fourth? The document justifying the act of Congress-you know it as Thomas Jefferson’s Declaration of Independence-was adopted on the fourth, as is indicated on the document itself, which is, one supposes, the cause for all the confusion.
As one scholar has observed, what has happened is that the document announcing the event has overshadowed the event itself.