Twelve colonies sent delegates to the First Continental Congress in 1774.
The congress met in Philadelphia from September 5 to October 26, 1774, in response to Britain’s Coercive Acts and the growing crisis between the colonies and Parliament. Delegates attended from every colony except Georgia, which did not yet join the collective resistance.
This is why sources often describe the gathering as representing twelve of the Thirteen Colonies. The absence of Georgia is an important detail that can be lost when the event is summarized as a meeting of all the colonies.
The congress did not declare independence. Its major actions included adopting the Continental Association, which organized a boycott of British goods, and sending a petition to King George III. The later Second Continental Congress, convened in 1775, directed the war effort and eventually approved independence.