| 105781 | September 15 | Holiday and observance | Earliest day on which German-American Steuben Parade can fall, while September 21 is the latest celebrated on the third Saturday in September. (United States, especially New York City) |
| 105782 | September 15 | Holiday and observance | Earliest day on which POW/MIA Recognition Day can fall, while September 21 is the latest celebrated on the third Friday in September. (United States) |
| 105783 | September 15 | Holiday and observance | Earliest day on which Prinsjesdag can fall, while September 21 is the latest celebrated on the third Tuesday in September. (Netherlands) |
| 105784 | September 15 | Holiday and observance | Earliest day on which Respect for the Aged Day can fall, while September 21 is the latest celebrated on the third Monday in September. (Japan) |
| 105785 | September 15 | Holiday and observance | Battle of Britain Day (United Kingdom) |
| 105786 | September 15 | Holiday and observance | Children's Day (Nepal) (celebrated on the 15th on leap years) |
| 105787 | September 15 | Holiday and observance | Engineer's Day (India) |
| 105788 | September 15 | Holiday and observance | Free Money Day (International) |
| 105789 | September 15 | Holiday and observance | Independence Day, celebrates the independence of Guatemala (a Patriotic Day), El Salvador, Honduras, Nicaragua, and Costa Rica from Spain in 1821. |
| 105790 | September 15 | Holiday and observance | International Day of Democracy (International) |
| 105791 | September 15 | Holiday and observance | Knowledge Day (Azerbaijan) |
| 105792 | September 15 | Holiday and observance | Restoration of Primorska to the Motherland Day (Slovenia) |
| 105793 | September 15 | Holiday and observance | Silpa Bhirasri Day (Thailand). |
| 105794 | September 15 | Holiday and observance | The beginning of National Hispanic Heritage Month, celebrated until October 15 (United States) |
| 105795 | September 15 | Holiday and observance | World Lymphoma Awareness Day (International) |
| 105796 | September 16 | Event | 307 – Emperor Severus II is captured and imprisoned at Tres Tabernae. He is later executed (or forced to commit suicide) after Galerius unsuccessfully invades Italy. |
| 105797 | September 16 | Event | 1400 – Owain Glyndŵr is declared Prince of Wales by his followers. |
| 105798 | September 16 | Event | 1620 – Pilgrims set sail from England on the Mayflower. |
| 105799 | September 16 | Event | 1701 – James Francis Edward Stuart, sometimes called the "Old Pretender", becomes the Jacobite claimant to the thrones of England and Scotland. |
| 105800 | September 16 | Event | 1776 – American Revolutionary War: The Battle of Harlem Heights is fought. |
| 105801 | September 16 | Event | 1779 – American Revolutionary War: The Franco-American Siege of Savannah begins. |
| 105802 | September 16 | Event | 1795 – The first occupation by United Kingdom of Cape Colony, South Africa with the Battle of Hout Bay, after successive victories at the Battle of Muizenberg and Wynberg, after William V requested protection against revolutionary France's occupation of t |
| 105803 | September 16 | Event | 1810 – With the Grito de Dolores, Father Miguel Hidalgo begins Mexico's fight for independence from Spain. |
| 105804 | September 16 | Event | 1812 – The Fire of Moscow begins shortly after midnight and destroys three quarters of the city days later. |
| 105805 | September 16 | Event | 1863 – Robert College of Istanbul-Turkey, the first American educational institution outside the United States, is founded by Christopher Robert, an American philanthropist. |
| 105806 | September 16 | Event | 1880 – The Cornell Daily Sun prints its first issue in Ithaca, New York. The Sun is the nation's oldest, continuously-independent college daily. |
| 105807 | September 16 | Event | 1893 – Settlers make a land run for prime land in the Cherokee Strip in Oklahoma. |
| 105808 | September 16 | Event | 1908 – The General Motors Corporation is founded. |
| 105809 | September 16 | Event | 1919 – The American Legion is incorporated. |
| 105810 | September 16 | Event | 1920 – The Wall Street bombing: A bomb in a horse wagon explodes in front of the J. P. Morgan building in New York City killing 38 and injuring 400. |