At the time of the Declaration of…
July 1776 CE
The flag contemporaneously known as "the Continental Colors" has historically been referred to as the first national flag.
The Continental Navy raises the Colors as the ensign of the fledgling nation in the American War for Independence—likely with the expedient of transforming their previous British red ensigns by adding white stripes—and will use this flag until 1777, when it would form the basis for the subsequent de jure designs.