Most delegates signed the engrossed Declaration of Independence on August 2, 1776, distinct from its July 4 adoption celebrated by America250.
Congress adopted the Declaration on July 4, but the parchment copy that is now famous was prepared and signed later. Most historians conclude that the principal signing ceremony took place on August 2, after Congress had ordered an engrossed copy on parchment. Additional delegates may have signed later when they were present.
The confusion comes partly from the date written on the document and from later recollections by Thomas Jefferson, John Adams, and Benjamin Franklin. Those men associated the signing with July 4, while other evidence shows that not every delegate was present in Congress on that day.
The engrossed document carries 56 signatures. John Hancock’s large signature became especially famous, but the signatures represented delegates from the colonies that had joined the independence decision. America250 commemorates the July 4 adoption, not a claim that every signature was placed on that date.