The Continental Congress adopted the Lee Resolution declaring independence on July 2, 1776.
Richard Henry Lee of Virginia introduced the resolution on June 7, 1776. Its central proposal stated that the United Colonies should become free and independent states, ending their political connection with Great Britain.
Congress approved the independence resolution on July 2. It then spent additional time editing and approving a separate explanatory document: the Declaration of Independence. That document was adopted on July 4, which is why Independence Day is celebrated on July 4 rather than July 2.
John Adams famously predicted that July 2 would be remembered as a great anniversary festival. His prediction was close but not correct because the public associated the national celebration with the date of the Declaration’s adoption and publication.