The design of the flag has been modified 26 times officially since 1777. The 48-star flag was in effect for 47 years until the 49-star version became official on July 4, 1959. The 50-star flag was ordered by President Eisenhower on August 21, 1959 and was adopted in July 1960. It is the longest-used version of the U.S. flag and has been in use for over 54 years.
Data Source: https://en.wikipedia.org/wiki/Flag_of_the_United_States
Two little known facts:
1) after the first 15 states became actual states (Connecticut, Delaware, Georgia, Maryland, Massachusetts, New Hampshire,New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, Virginia,Vermont, Kentucky) – all new states became states on July 4th of their respective years.
2) when Alaska became a state on July 4th, 1959 there was a 49 star flag used as the US flag for 1 year. It consisted of 7 rows of starts with 7 stars in every other row was offset by 1 star width.
On July 4th, 1960 – Hawaii became a state and the current flag was introduced which created our current stars and stripes edition!