| 108811 | September 23 | Event | 1459 – Battle of Blore Heath, the first major battle of the English Wars of the Roses, is fought at Blore Heath in Staffordshire. |
| 108812 | September 23 | Event | 1568 – Spanish naval forces rout an English fleet, under the command of John Hawkins, at the Battle of San Juan de Ulúa near Veracruz. |
| 108813 | September 23 | Event | 1641 – The Merchant Royal, carrying a treasure worth over a billion US dollars, is lost at sea off Land's End. |
| 108814 | September 23 | Event | 1642 – First commencement exercises occur at Harvard College. |
| 108815 | September 23 | Event | 1779 – American Revolution: John Paul Jones on board the USS Bonhomme Richard wins the Battle of Flamborough Head. |
| 108816 | September 23 | Event | 1780 – American Revolution: British Major John André is arrested as a spy by American soldiers exposing Benedict Arnold's change of sides. |
| 108817 | September 23 | Event | 1803 – Second Anglo-Maratha War: Battle of Assaye between the British East India Company and the Maratha Empire in India. |
| 108818 | September 23 | Event | 1806 – Lewis and Clark return to St. Louis after exploring the Pacific Northwest of the United States. |
| 108819 | September 23 | Event | 1821 – Tripolitsa, Greece, is captured by Greek rebels during the Greek War of Independence. |
| 108820 | September 23 | Event | 1845 – The Knickerbockers Baseball Club, the first baseball team to play under the modern rules, is founded in New York. |
| 108821 | September 23 | Event | 1846 – Astronomers Urbain Jean Joseph Le Verrier, John Couch Adams and Johann Gottfried Galle collaborate on the discovery of Neptune. |
| 108822 | September 23 | Event | 1868 – Grito de Lares ("Lares Revolt") occurs in Puerto Rico against Spanish rule. |
| 108823 | September 23 | Event | 1889 – Nintendo Koppai (Later Nintendo Company, Limited) is founded by Fusajiro Yamauchi to produce and market the playing card game Hanafuda. |
| 108824 | September 23 | Event | 1899 – American Asiatic Squadron destroys a Filipino battery at the Battle of Olongapo. |
| 108825 | September 23 | Event | 1905 – Norway and Sweden sign the "Karlstad treaty", peacefully dissolving the Union between the two countries. |
| 108826 | September 23 | Event | 1908 – University of Alberta in Alberta, Canada, is founded. |
| 108827 | September 23 | Event | 1909 – The Phantom of the Opera (original title: Le Fantôme de l'Opéra), a novel by French writer Gaston Leroux, is first published as a serialization in Le Gaulois. |
| 108828 | September 23 | Event | 1911 – Pilot Earle Ovington makes the first official airmail delivery in America under the authority of the United States Post Office Department |
| 108829 | September 23 | Event | 1913 – Roland Garros of France becomes the first to fly in an airplane across the Mediterranean (from St. Raphael France to Bizerte, Tunisia). |
| 108830 | September 23 | Event | 1932 – The Kingdom of Hejaz and Nejd is renamed the Kingdom of Saudi Arabia. |
| 108831 | September 23 | Event | 1936 – First ascent of Siniolchu by a German team. |
| 108832 | September 23 | Event | 1938 – Mobilization of the Czechoslovak army in response to the Munich Crisis. |
| 108833 | September 23 | Event | 1942 – World War II: The Matanikau action on Guadalcanal begins: U.S. Marines attack Japanese units along the Matanikau River. |
| 108834 | September 23 | Event | 1943 – World War II: The Nazi puppet state the Italian Social Republic is founded. |
| 108835 | September 23 | Event | 1950 – Korean War: The Battle of Hill 282: The first US friendly-fire incident on British military personnel since World War II occurs. |
| 108836 | September 23 | Event | 1952 – Richard Nixon makes his "Checkers speech". |
| 108837 | September 23 | Event | 1959 – Iowa farmer and corn breeder Roswell Garst hosts Soviet premier Nikita Khrushchev. |
| 108838 | September 23 | Event | 1959 – The MS Princess of Tasmania, Australia's first passenger roll-on/roll-off diesel ferry, makes her maiden voyage across Bass Strait. |
| 108839 | September 23 | Event | 1962 – The Lincoln Center for the Performing Arts opens in New York City. |
| 108840 | September 23 | Event | 1969 – The Chicago Eight trial opens in Chicago. |