On July 2, 1776 representatives of the 13 colonies voted in favor of independence. Two days later, on July 4th, 1776, these representatives also know as the Continental Congress adopted the Declaration of Independence.
Already embattled with Great Britain since April 1775, the Continental Congress began exploring independence from Britain in early June of 1776. The Virginia delegate, Richard Henry Lee, introduced the initial resolution calling for independence in early June of 1776. After much debate, a vote on the resolution was postponed, but a five-man committee was tasked with drafting a formal statement justifying a break with Britain. On this committee were John Adams of Massachusetts, Benjamin Franklin of Pennsylvania, Thomas Jefferson of Virginia, Robert Livingston of New York and Robert Sherman of Connecticut. From this group came the Declaration of Independence largely written by Thomas Jefferson.
The first commemoration of American independence was celebrated in Philadelphia on July 4th 1777 and Massachusetts became the first state to make the 4th of July an official holiday. In 1870 Independence Day became an official US holiday and then in 1941 it became a paid holiday for government employees.
Original celebrations during the War of Independence included mock funerals of King George III, parades, concerts, bonfires, mock firings of cannons and muskets (with probably some real musket firings too). Today parades, concerts, firework shows, barbecues, and family gatherings have become symbolic of this mid-summer day.