Shown here are the 27 legal flags flown throughout our history, with effective date(s) and state addition(s) that changed the star field. By law, a star is added to the U.S. Flag on the 4th of July following the admission of a State(s) to the Union. Contrary to popular belief, the first official U.S. Flag was not the Betsy Ross Flag (13 stars in a circle) but the staggered star pattern shown in the below 13-star flag.
It is important to note that no U.S. Flag ever becomes obsolete. Each flag shown is still a legal flag and may be flown at any time.