| January 1 | Haiti gains independence from France (National Day) |
| January 5 | Ohio legislature passes 1st laws restricting free blacks movement |
| January 30 | Mungo Park leaves England seeking source of Niger River |
| January 31 | British Vice-Admiral William Blighs fleet reaches Curacao |
| February 15 | New Jersey becomes last northern state to abolish slavery |
| February 16 | Lt. Stephen Decatur raids Tripoli Harbor and burns Navy frigate "Philadelphia" after pirates seized it |
| February 18 | 1st U.S. land-grant college, Ohio University, Athens Ohio, chartered |
| February 21 | 1st locomotive, Richard Trevithick's, runs for 1st time, in Wales |
| February 23 | Conspirators against Napoleon, for restoration of Louis XVIII |
| February 25 | Jefferson nominated for president at Democratic-Republican caucus |
| February 26 | Vice-Admiral William Bligh ends siege of Fort Amsterdam, Willemstad |
| March 17 | Johann von Schiller's "Wilhelm Tell," premieres |
| March 21 | French civil Code of Napoleon adopted |
| March 26 | Congress orders removal of Indians east of Mississippi to Louisiana |
| March 26 | Territory of Orleans organizes in Louisiana Purchase |
| March 28 | Ohio passed law restricting movement of Blacks, 1804 |
| March 29 | Thousands of Whites massacred in Haiti |
| April 22 | Gioacchino Rossini (12) performs in Imola |
| April 28 | 31 English ship sail Suriname river demand transition colony |
| April 30 | Hague's Theater opens |
| May 6 | Suriname sold to English, until February, 1816 |
| May 14 | Lewis and Clark set out from St. Louis for Pacific Coast |
| May 16 | Senate and Tribune declare Napolean leader of France |
| May 17 | Lewis and Clark begin exploration of Louisiana Purchase |
| May 18 | Napoleon Bonaparte proclaimed Emperor of France |
| May 21 | Lewis and Clark Expedition begins |
| June 15 | 12th amendment ratified; deals with manner of choosing president |
| August 25 | Alice Meynell becomes 1st woman jockey (England) |
| September 25 | 12th amendment to U.S. constitution, regulating judicial power |
| October 2 | England mobilizes to protect against French invasion |
| October 9 | Hobart Tasmania founded |
| November 18 | Palver Purim 1st celebrated to commemorate miraculous escape |
| November 30 | Impeachment trial of Supreme Court Justice Samuel Chase begins |
| December 1 | Emperor Napoleon marries Josephine of Martinique |
| December 2 | Napoleon Bonaparte crowned emperor of France in Paris by Pope Pius VII |
| December 5 | Thomas Jefferson re-elected U.S. president/George Clinton vice-president |
