The rescue of crew of Pisces III in the Irish Sea
September 2: National Day in Vietnam (1945)
- 47 BC – Caesarion, a possible son of Julius Caesar, became the last king of the Ptolemaic dynasty of Egypt, ruling jointly with his mother Cleopatra.
- 1885 – White miners in Rock Springs, Wyoming, attacked Chinese-American immigrants, killing at least 28 Chinese miners and causing approximately $150,000 in property damage.
- 1945 – On the deck of the U.S. Navy battleship Missouri in Tokyo Bay, representatives from the Empire of Japan and the Allied powers signed the Japanese Instrument of Surrender (pictured), formally ending World War II.
- 2011 – Bad weather caused a Chilean Air Force aircraft to crash into the Pacific Ocean, killing all 21 people on board.
September 6: Defence Day in Pakistan (1965); Labour Day in Canada and Labor Day in the United States (2021)
September 7: First day of Rosh Hashanah (Judaism, 2021, AM 5782)
September 8: Victory Day in Malta
September 10: Ganesh Chaturthi begins (Hinduism, 2021)
- 1509 – A strong earthquake occurred in the Sea of Marmara, devastating much of Constantinople and causing at least 1,000 deaths.
- 1897 – A sheriff's posse fired on a peaceful labor demonstration mostly comprising Polish- and Slovak-American anthracite coal miners in Luzerne County, Pennsylvania, killing 19 people and wounding many others.
- 1946 – While riding a train to Darjeeling, India, Sister Teresa Bojaxhiu, later Mother Teresa (pictured), experienced what she later described as the "call within the call", directing her to "leave the convent and help the poor while living among them".
- 1961 – At the Italian Grand Prix at Monza, German driver Wolfgang von Trips's car collided with another, causing it to become airborne and crash into a side barrier, killing him and 15 spectators.
September 11: National Day of Catalonia
Orchestra assembled to perform Mahler's Symphony No. 8
September 13: Feast day of Saint John Chrysostom (Western Christianity)
Model of Luna 2
September 15: Battle of Britain Day in the United Kingdom (1940)
September 17: Constitution Day in the United States (1787)
September 19: Battle of Britain Day in Canada (2021); International Talk Like a Pirate Day
Great Buddha of Kamakura
September 21: International Day of Peace
Charles Edward Stuart
- 1170 – Norman invasion of Ireland: English and Irish forces conquered Dublin, forcing Ascall mac Ragnaill, the last Norse–Gaelic king of Dublin, into exile.
- 1745 – Jacobite risings: Jacobite troops led by Charles Edward Stuart (pictured) defeated Hanoverian forces in Prestonpans, Scotland.
- 1965 – Portugal accepted a diplomatic mission from Southern Rhodesia despite objections by Britain, which had required the colony to implement black majority rule as a condition of independence.
- 1999 – A 7.7 Mw earthquake struck Jiji, Taiwan, killing 2,415 people, injuring more than 11,000 others and causing about NT$300 billion (US$10 billion) in damage across the island.
September 22: Independence Day in Mali (1960); Baltic Unity Day in Latvia and Lithuania
Damage from the great fire of Smyrna
September 23: Celebrate Bisexuality Day
Nixon delivering the Checkers speech
September 24: Heritage Day in South Africa
Battle of San Juan de Ulúa
September 26: Banned Books Week begins (2021)
September 27: Meskel (Orthodox Tewahedo)
Locomotion No. 1
Juan Rodríguez Cabrillo
September 29: Michaelmas (Western Christianity)
Alouette 1 before launch
September 30: Orange Shirt Day in Canada