In the United States, Flag Day is celebrated on June 14, 2021. It commemorates the adoption of the flag of the United States, which happened that day by resolution of the Second Continental Congress in 1777. 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, though on June 14, 1937, Pennsylvania became the first (and only) U.S. state to celebrate Flag Day as a state holiday, beginning in the town of Rennerdale. Title 36 of the United States Code, Subtitle I, Part A, CHAPTER 1, § 110 is the official statute on Flag Day; however, it is at the President's discretion to proclaim officially the observance.
One of the longest-running Flag Day parades is held annually in Quincy, Massachusetts, which began in 1952 and celebrated its 57th year in 2009. The 59th Annual Appleton Wisconsin 2009 Flag Day Parade will feature the U.S. Navy. City of Appleton Wisconsin. The largest Flag Day parade is held annually in Troy, New York, which bases its parade on the Quincy parade and typically draws 50,000 spectators.
Perhaps the oldest, continuing Flag Day parade is at Fairfield WA. Beginning in 1909 or 1910, Fairfield has held a parade every year since, with the possible exception of 1918, and will celebrate the "Centennial" parade in 2010, along with some other commemorative events. (From: Wikipedia, license: CCA-SA)