The Declaration of Independence which is housed in the National Archives building here is actually a copy done by Thomas Jefferson.  The original was lost or destroyed.

1823 facsimile of the engrossed copy

The Declaration of Independence was a statement adopted by the Continental Congress on July 4, 1776, which announced that the thirteen American colonies, then at war with Great Britain, regarded themselves as independent states, and no longer a part of the British Empire. Instead they now formed a new nation--the United States of America. John Adams was a leader in pushing for independence, which was unanimously approved on July 2. A committee had already drafted the formal declaration, to be ready when congress voted on independence. Adams persuaded the committee to select Thomas Jefferson to compose the original draft of the document, which congress would edit to produce the final version. The Declaration was ultimately a formal explanation of why Congress had voted on July 2 to declare independence from Great Britain, more than a year after the outbreak of the American Revolutionary War. The national birthday, the Independence Day is celebrated on July 4, although Adams wanted July 2.

• http://en.wikipedia.org/wiki/United States Declaration of Independence