America's 250th anniversary commemorates the Declaration of Independence adopted on July 4, 1776.
The Second Continental Congress approved the Declaration in Philadelphia, at the Pennsylvania State House, now called Independence Hall. The document announced that the thirteen American colonies were separating politically from Great Britain and explained their reasons.
July 4 marks adoption of the final text, not necessarily the date when every delegate signed the parchment copy. Most delegates signed the engrossed document on August 2, 1776, while some signatures were added later. This distinction is a common source of confusion.
John Adams believed July 2 would become the great national holiday because Congress voted for independence on that date. Instead, July 4 became the celebrated anniversary because it is the date printed on the approved Declaration and associated with its public publication.