On 3 July 1776, John Adams wrote his wife, Abigail, a letter in two parts. In the morning he wrote, "Yesterday the greatest question was decided, which ever was debated in America, and a greater, perhaps, never was or will be decided among Men. A resolution was passed without one dissenting colony 'that these United Colonies are, and of right ought to be, free and independent states' ... You will see in a few days a declaration setting forth the causes which have impelled us to this mighty revolution and the reasons which will justify it in the sight of God and man."
Later that evening he added that "the Second Day of July, will be the most memorable Epocha, in the History of America. I am apt to believe that it will be celebrated, by succeeding Generations, as the great anniversary Festival. It ought to be commemorated, as the day of Deliverance by solemn Acts of Devotion to God Almighty. It ought to be solemnized with Pomp and Parade, with Shews, Games, Sports, Guns, Bells, Bonfires and Illuminations from one end of this Continent to the other from this Time forward forever more."
The "Declaration of Independency" (as Adams called it in the same letter) was passed by the Second Continental Congress on 2 July 1776, and approved by all but one of the thirteen colonies on 4th of July. The delegates from New York, who weren't sure they had the authority to approve on behalf of the colony, signed on 9 July.
You can read the evening portion of the original letter by clicking on the following link of the Massachusetts Historical Society.