As per Wikipedia:
"In the United States Flag Day is celebrated on June 14. It commemorates the adoption of the flag of the United States, which happened that day by resolution of the Second Continental Congress in 1777.The United States Army also celebrates the Army 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.
The week of June 14 is designated as "National Flag Week." During National Flag Week, the president will issue a proclamation urging U.S. citizens to fly the American flag for the duration of that week. The flag should also be displayed on all government buildings. Some organizations hold parades and events in celebration of America's national flag and everything it represents."