Flag Day commemorates the adoption of the flag of the United States, which
happened on that day in 1777 by resolution of the Second Continental Congress.

The United States Army also celebrates it’s Birthday on this date; Congress adopted
"the American continental army" after reaching a consensus position in the Committee
of the Whole on June 14, 1775.

In 1916, President Woodrow Wilson issued a proclamation that officially established
June 14 as Flag Day; in August 1949, National Flag Day was established by an Act
of Congress. Flag Day is not an official federal holiday.