The United States Declaration of Independence was adopted on July 4, 1776, the date commemorated by America250.
The Second Continental Congress approved the final wording in Philadelphia. The declaration announced that the thirteen colonies regarded themselves as independent states rather than British colonies. July 4 is therefore celebrated as Independence Day in the United States.
A common mix-up concerns July 2. Congress voted for independence on July 2, but it adopted the formal declaration on July 4. The document was engrossed and signed later, beginning with John Hancock and eventually involving 56 delegates. America250 marks the 250th anniversary of the 1776 adoption, not the date on which every signer added a signature.