Portal:United States/Anniversaries/September/September 20
- 1814 – Francis Scott Key's poem Defence of Fort McHenry (pictured), which would later become known as "The Star Spangled Banner", was published for the first time, in the broadsheet publication Patriot.
- 1848 – The American Association for the Advancement of Science is created.
- 1881 – Chester A. Arthur is inaugurated as the 21st President of the United States following the assassination of James Garfield.
- 1891 – The first gasoline-powered car debuts in Springfield, Massachusetts.
- 1973 – Billie Jean King beats Bobby Riggs in The Battle of the Sexes tennis match at the Houston Astrodome in Houston, Texas.
- 2001 – In an address to a joint session of Congress and the American people, U.S. President George W. Bush declares a "war on terror".