Resolved, that the flag of the United States be thirteen stripes, alternate red and white; that the union be thirteen stars, white in a blue field representing a new constellation."
-Marine Committee of the Second Continental Congress, June 14, 1777
The first flag day was celebrated on June 14, 1777. It wasn't officially recognized until President Truman signed it into law in 1949. The law was proposed. Bernard Cigrand, known as the "Father of Flag Day" went around the country delivering speeches about having a Flag Day. He first observed in 1885 in the city of Waubeka, Wisconsin.
There were many other proponents including President Woodrow Wilson. The in 1927 President Coolidge offered the second proclamation but it wasn't until 1949 that it became law.