National Flag Day commemorates the anniversary of Congress’s adoption of the “stars and stripes” design for the U.S. flag in 1777. On June 14, 1885, Bernard Cigrand, a young teacher in Wisconsin, asked his students to observe this anniversary and began his efforts to bring about a national observance of Flag Day. In 1916, President Wilson issued a proclamation calling for a national observance of Flag Day, and in 1949, President Truman signed a legislation officially designating June 14 as National Flag Day.
Learn more about the history of National Flag Day here.
Sources: timeanddate.com, nationalflagday.com