When did Louisiana get a star on the U.S. flag?

April 30, 1812  – Louisiana officially became a State.  The 18th State.

The American Flag started out with 13 stars.

Following the 13-star flag, a 15-Star version of the U.S. flag was born in 1795 and was the flag which inspired Francis Scott Key to write “The Star Spangled Banner,” a song destined to become the national anthem of the new born nation.

In the following years the flag did not change until 1818, when a plan was passed by Congress at the suggestion of U.S. Naval Captain Samuel C. Reid. This act increased the star count on the flag to 20, while maintaining the original thirteen stripes to symbolize the original thirteen colonies. The act also included a provision stating that as new states are admitted to the union, a new star would be added to the flag on the following Fourth of July.

So the first flag to have enough stars on it to include Louisiana was in 1818 with 20 stars.

In 1819 Illinois was the first  State to be added after the Fourth of July provision.  Resulting in…you got it…a flag with 21 stars.

Thus,  Sayest the Interwebs.