On June 14, 1777, the Continental Congress passed a resolution setting the design for the U.S. flag. Celebrations of this date go back to the late 1800s, but it wasn’t until 1949 that President Harry Truman signed the national observance into law. Read the history from the U.S. Department of Veterans Affairs.
On June 14, 1904, The Wyoming Tribune proclaimed the celebration on its front page. (From Wyoming Newspapers.)