Events
- 1775 – The birth of what would later become the United States Post Office Department was established by the Second Continental Congress.
- 1788 – New York ratifies the United States Constitution and becomes the 11th state of the United States.
- 1861 – American Civil War: George B. McClellan assumes command of the Army of the Potomac following a disastrous Union defeat at the First Battle of Bull Run.
- 1863 – American Civil War: Morgan's Raid ends – At Salineville, Ohio, Confederate cavalry leader John Hunt Morgan and 360 of his volunteers are captured by Union forces.
- 1878 – In California, the poet and American West outlaw calling himself "Black Bart" makes his last clean getaway when he steals a safe box from a Wells Fargo stagecoach. The empty box will be found later with a taunting poem inside.
- 1908 – United States Attorney General Charles Joseph Bonaparte issues an order to immediately staff the Office of the Chief Examiner (later renamed the Federal Bureau of Investigation).
- 1941 – World War II: In response to the Japanese occupation of French Indo-China, US President Franklin D. Roosevelt orders the seizure of all Japanese assets in the United States.
- 1945 – The US Navy cruiser Indianapolis arrives at Tinian with the warhead for the Hiroshima atomic bomb.
- 1946 – Aloha Airlines began service from Honolulu International Airport.
- 1947 – U.S. President Harry S. Truman signs the National Security Act into law, creating the Central Intelligence Agency, reorganizing the U.S. Armed Forces, and establishing the Joint Chiefs of Staff.
- 1948 – U.S. President Harry S. Truman signs Executive Order 9981 desegregating the military of the United States.
- 1953 – Arizona Governor John Howard Pyle orders an anti–polygamy law enforcement crackdown on residents of Short Creek, Arizona, which becomes known as the Short Creek Raid.
- 1958 – Explorer program: Explorer 4 is launched.
- 1963 – Syncom 2, the world's first geosynchronous satellite, is launched from Cape Canaveral on a Delta B booster.
- 1971 – Apollo Program: Apollo 15 Mission – Launch of Apollo 15.
- 1989 – A federal grand jury indicts Cornell University student Robert T. Morris, Jr. for releasing the Morris worm, thus becoming the first person to be prosecuted under the 1986 Computer Fraud and Abuse Act.
- 1990 – The Americans with Disabilities Act of 1990 was signed into law by President George H. W. Bush.
- 2005 – Space Shuttle program: STS-114 Mission – Launch of Discovery, NASA's first scheduled flight mission after the Columbia Disaster in 2003.