1801 1802 1803 - 1804 - 1805 1806 1807
| Decades: |
1770s 1780s 1790s - 1800s - 1810s 1820s 1830s
| Centuries: |
18th century - 19th century - 20th century
- January 1 - End of French rule in Haiti
- June 15 - The Twelfth Amendment to the U.S. Constitution ratified by New Hampshire, and arguably becomes effective (subsequently vetoed by the Governor of New Hampshire)
- July 27 - The Twelfth Amendment to the U.S. Constitution ratified by Tennessee, removing doubt surrounding adoption.
- February 14 - First Serbian Uprising began.
- February 15 - New Jersey becomes the last northern state to abolish slavery
- February 16 - First Barbary War: Stephen Decatur leads a raid to burn the pirate-held frigate Philadelphia.
- February 21 - The first self-propelling steam engine or steam locomotive makes its outing at the Pen-y-Darren ironworks in Wales. Designed by Richard Trevithick, a Cornishman.
- March 7 – John Wedgwood founds The Royal Horticultural Society
- March 10 - Louisiana Purchase: In St. Louis, a formal ceremony is conducted to transfer ownership of Louisiana Territory from France to the United States.
- March 20 – Execution of the Duc d’Enghien for plotting against Napoleon
- March 21 - Code Napoleon adopted as French civil law
- April 26 – Henry Addington resigns as Prime Minister of the United Kingdom
- May 10 - William Pitt the younger begins his second term as a Prime Minister of the United Kingdom
- May 14 - The Lewis and Clark Expedition departs from Camp Dubois and begin their historic journey by traveling up the Missouri River.
- May 18 - Napoleon Bonaparte is proclaimed Emperor of France by the French Senate.
- August 20 - Lewis and Clark Expedition: The "Corps of Discovery", whose purpose is to explore the Louisiana Purchase, suffers it first and last death when Sergeant Charles Floyd dies, apparently from acute appendicitis.
- September 1 - German astronomer K. L. Harding discovers the asteroid Juno
- November - Thomas Jefferson defeats Charles C. Pinckney in U.S. presidential election
- November 30 - The Jeffersonian Republican-controlled United States Senate begin an impeachment trial against Federalist-partisan Supreme Court of the United States Justice Samuel Chase (he was charged with political bias but was acquitted by the Senate of all charges on March 1, 1805).
- December 2 - At Notre Dame Cathedral in Paris, Napoleon Bonaparte crowns himself as the first Emperor of France in a thousand years (the Napoleonic Code is adopted).
- December 12 - Spain declares war on Britain
- [[P�re Lachaise|P�re Lachaise Cemetery]] a 118 acre (0.5 km²) cemetery in Paris, France was founded.
- March 14 - Johann Strauss I, Austrian composer
- March 17 - Jim Bridger, pioneer (d. 1881)
- July 1 - George Sand (Amantine Aurore Lucile Dupin), writer
- July 4 - Nathaniel Hawthorne, writer
- July 28 - Ludwig Feuerbach, German Philosopher
- November 23 - Franklin Pierce, 14th president of the United States
- December 21 - Benjamin Disraeli, British politician, writer
- February 12 - Immanuel Kant, German philosopher
- September 4 - Richard Somers, American naval officeraf:1804
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