Antique American flags are highly desirable collectibles, and many are worth thousands. Since a star is added for each state and 29 states were admitted during the 19th century, flag designs had to be changed often. It wasn't until 1818 that Congress passed a bill that set the number of stripes to 13 and declared that a new star be added on the Fourth of July after the admission of a new state. There was no standard star arrangement until the 48-star flag in 1912, so many versions of early flags were made. For example, on the 20-star flag used from 1818-1819, some were made with a rectangular star arrangement, while others have the stars arranged like an actual star. Some designs lasted only a year, making many star arrangements extremely rare and valuable. Since each star represents a state, you can date an old flag by counting the number of stars on your flag.
The idea for a day to celebrate the flag started in 1885, when a Wisconsin schoolteacher arranged for his pupils to celebrate "Flag Birthday." It commemorates the adoption of the 13-star and 13-stripe flag of the United States on June 14, 1777. It wasn't until 1916 that Flag Day was made an official holiday by President Wilson, and not until 1949 that President Truman designated the holiday to be celebrated on June 14th.