Flag Day in the United States is an unofficial holiday commemorating the adoption of the American flag 244 years ago by the Second Continental Congress on June 14, 1777. The U.S. flag has gone through many iterations over the years, with Congress ordering changes in its design up until 1960, including the addition of stars whenever a new state joined the union. Todayâs flag has 13 horizontal stripes, representing the original 13 colonies and 50 stars representing the 50 states.