From The American Patriot’s Almanac:
“On June 14, 1777, during the Revolutionary War, the Continental Congress in Philadelphia adopted the Stars and Stripes as the official national flag.
‘Resolved, that the Flag of the thirteen United States be thirteen stripes, alternate red and white; that the Union be thirteen stars, white on a blue field, representing a new constellation.’
Congress gave no further instruction as to exactly what the flag should look like, such as its dimensions or how the stars should be arranged. Consequently, early U.S. flags did not all look alike. Some flags had stars with six points, others with eight. Some flag makers sewed the stars in rows on the blue field, others in a circle or scattered without an organized pattern.
The first official, widespread observance of the flag’s birthday came on June 14, 1877, when the flag was one hundred years old. Over the next several years, many schools, veterans groups, and patriotic societies turned the day into a yearly celebration. Mayors and governors began to issue proclamations calling for parades and patriotic events on June 14.
In 1916, President Woodrow Wilson established Flag Day as an annual national celebration. In 1949 Congress and President Truman officially made June 14 a permanent yearly observance.