The Lee Resolution declared the American colonies free and independent states before the Declaration of Independence.
The Second Continental Congress adopted the resolution on July 2, 1776. It was introduced by Virginia delegate Richard Henry Lee and stated that the United Colonies should be free and independent states, severing political ties with Great Britain.
Congress then debated and approved the Declaration of Independence on July 4. The Declaration served as a public explanation of the decision already expressed in the Lee Resolution, including its arguments about rights and grievances.
The July 2 vote is why John Adams believed independence should be celebrated on that date. In practice, July 4 became the national holiday because it is the date printed on the Declaration and associated with its adoption.