The engrossed parchment copy of the United States Declaration of Independence was mainly signed on August 2, 1776.
Congress adopted the Declaration on July 4, 1776, but adoption and signing were separate steps. The approved text had to be prepared as an official engrossed parchment document before most delegates could sign it. Historians generally identify August 2 as the principal signing date.
The common association between the Declaration and July 4 is therefore accurate for its adoption and public anniversary, but not necessarily for the main signing ceremony. Some delegates were absent on August 2, and additional signatures may have been added afterward.
This distinction explains why the document itself bears the date July 4 while historical accounts often give August 2 for the signing. The anniversary celebrated by America250 is based on the July 4 adoption date.