The Continental Congress adopted the Declaration of Independence on July 4, 1776, in the Pennsylvania State House (now Independence Hall) in Philadelphia. But that date marks the approval of the text, not the ceremony most people picture.
The famous signing — the one with John Hancock's enormous signature at the center — took place on August 2, 1776, after the engrossed parchment copy was ready. Not every signer was present that day. Several delegates signed weeks or even months later when they finally arrived in Philadelphia.
Contrary to popular belief, there was no single dramatic moment when all 56 men lined up to sign. It was a process that stretched from early July into the fall of 1776, as delegates came and went and the parchment was passed around.