Why is Independence Day usually called the Fourth of July?

What is the real the day that we historically celebrated Independence Day? I have read that the Federalists used the fourth of July and the Republicans (now called Democrats) used the first day of May at least prior to 1800.

• Answer:

  In 1776, John Adams wrote to his wife about celebrating on July 2nd - the day the resolution for independence was approved. However, July 4th, the day the Declaration of Independence was approved, has been the day of celebration since 1777 (the first anniversary).  This happened in part by accident:  Congress didn't think to mark the anniversary at all until July 3rd, so the 2nd had already passed, leaving the 4th. For a very interesting overview of how the Declaration itself, and not the independence it declared, came to captivate the American imagination, please read the following article: http://iipdigital.usembassy.gov/st/english/texttrans/2005/06/20050606131757pssnikwad0.3779871.html#axzz2xJQrqfhu (If the link takes you to the main site and not the article, just search for "Making Sense of the Fourth of July.")