1805
After thirteen years the First French Empire abolished the French Republican Calendar in favour of the Gregorian calendar.
Events
January–March
- January 11 - The Michigan Territory is created.
- February 7 - King Anouvong becomes ruler of Vientiane on the death of his brother Inthavong.
- February 15 - The Harmony Society is officially formed as a Christian community in Harmony, Pennsylvania.
- March 1 - Justice Samuel Chase is acquitted of impeachment charges by the United States Senate.
- March 4 - Thomas Jefferson is sworn in for a second term as President of the United States.
- March 5 - The New Brunswick Legislature passes a bill to advance literacy in the province, which eventually leads to the creation of public education in Canada.
April–June
- April 7 - Beethoven's Symphony No. 3, Eroica, has its public premiere at the Theater an der Wien in Vienna under his baton.
- April 27 - Battle of Derne: United States Marines and Berbers attack the Tripolitan city of Derna.
- April 29 - Rutger Jan Schimmelpenninck is appointed as Grand Pensionary of the Batavian Republic by Napoleon.
- May 26 - Napoleon is crowned King of Italy.
- May 31-June 2 - Napoleonic Wars: Battle of Diamond Rock - A Franco-Spanish fleet captures the strategic island of Diamond Rock off Martinique in the West Indies, from the British.
- June 1 - Tuscan-born composer Luigi Boccherini is buried in the Basílica pontificia de San Miguel in Madrid after being found dead on May 28.
- June 4
- * The First Barbary War ends between Tripoli and the United States of America.
- * The first Trooping the Colour ceremony is held at the Horse Guards Parade in London.
- * Detroit burns to the ground; most of the city is destroyed.
- June 13 - Lewis and Clark Expedition in the United States: Scouting ahead of the expedition, Meriwether Lewis and four companions sight the Great Falls of the Missouri River, confirming they are heading in the right direction.
July–September
- July 9 - Muhammad Ali Pasha founds his dynasty in Egypt.
- July 26 - 1805 Molise earthquake: 5,573 people in Molise and Campania, Italy, are killed.
- August 12 - Lewis and Clark Expedition: U.S. Army Captain Meriwether Lewis becomes the first white person to reach the Continental Divide of the Americas, crossing to the west at Lemhi Pass.
- August 29 - Emperor Franz I of Austria and his council of ministers vote in favor of going to war with France.
- August 31 - British Army General David Baird departs from Cork, leading an expedition to capture the Cape of Good Hope. Their ship arrives on January 4.
- September 21 - King Ferdinand of Naples signs a treaty in Paris agreeing to keep Naples neutral during the war between France and the allied powers.
- September 29 - Admiral Nelson of the British Royal Navy takes command of the fleet off of the coast of Cadiz, in order to counteract the navies of France and Spain.
October–December
- October 14 - Napoleonic Wars - War of the Third Coalition - Ulm Campaign - Battle of Elchingen: An Austrian corps under Johann von Riesch is defeated by Marshal Ney, near Elchingen, Bavaria.
- October 16-19 - War of the Third Coalition - Ulm Campaign - Battle of Ulm: Austrian General Mack von Leiberich is forced to surrender his entire army to Napoleon, after being surrounded.
- October 21 - Napoleonic Wars - War of the Third Coalition - Battle of Trafalgar: The British fleet, led by Admiral Horatio Nelson, defeats a combined French and Spanish fleet off the coast of Spain; however, Admiral Nelson is fatally shot.
- October 31 - Sweden, led by King Gustav IV Adolf, declares war on France.
- November 7 - The Lewis and Clark Expedition arrives at the Pacific Ocean.
- November 11 - Napoleonic Wars - Battle of Dürenstein: 8,000 French troops attempt to slow the retreat of a vastly superior Russian and Austrian force.
- November 16 - Napoleonic Wars - Battle of Schöngrabern: Russian forces, under Pyotr Bagration, delay the pursuit by French troops under Joachim Murat.
- November 20 - Beethoven's only opera Fidelio, in its original form, is premiered at the Theater an der Wien in Vienna, which at this time is under French military occupation.
- November 26 - The Pontcysyllte Aqueduct is opened in Wales; it is long and tall.
- December 2 - Napoleonic Wars: Battle of Austerlitz - French troops under Napoleon decisively defeat a joint Russo-Austrian force.
- December 26 - The Peace of Pressburg between France and Austria is signed in the Primate's Palace, Pressbury.
- December 31 - The French Republican Calendar is used for the last time, 8 days after being annulled by Napoleon, with the final official date being "9 Nivôse in Year XIV of the Revolution".
Date unknown
- James Squire becomes the first brewer in Australia to cultivate hops.
- The Old Man of the Mountain, a natural rock formation in the U.S. state of New Hampshire, is first mentioned by two workmen, Francis Whitcomb and Luke Brooks.
- Napoleon orders his soldiers to be vaccinated.
Births
January–June
- January 8 - Orson Hyde, American religious leader
- January 27 - Samuel Palmer, English artist
- February 13 - Peter Gustav Lejeune Dirichlet, German mathematician
- February 18 - Louis M. Goldsborough, United States Navy admiral
- March 3 - Jonas Furrer, first President of the Swiss Confederation
- March 14 - Eduard Clam-Gallas, Austrian general
- March 22 - Benito de Soto, Galician pirate
- March 23 - Sears Cook Walker, American mathematician, astronomer
- March 26 - Shirali Muslimov, Azerbaijani supercentenarian
- April 2 - Hans Christian Andersen, Danish writer
- April 8 - Hugo von Mohl, German botanist
- April 22 - Benito de Soto, Galician pirate
- June 9 - José Trinidad Cabañas, Honduran general, president and national hero
- June 22 - Giuseppe Mazzini Italian patriot, statesman and writer
July–December
- July 5 - Robert FitzRoy, English meteorologist, captain and politician
- July 29 - Alexis de Tocqueville, French historian
- July 30 - Rudolf Wagner, German anatomist, pathologist
- August 4 - William Rowan Hamilton, Irish physicist
- September 19 - John Stevens Cabot Abbott, American historian, pastor and pedagogical writer
- September 27 - George Müller, Prussian evangelist, founder of the New Orphan Houses, Ashley Down, Bristol in England
- November 14 - Fanny Mendelssohn, German composer, pianist
- November 28 - John Lloyd Stephens, American traveler, diplomat and Mayanist archaeologist
- December 2 - Cicero Price, American commodore
- December 10 - William Lloyd Garrison, American abolitionist
- December 12 - Henry Wells, American businessman, founder of Wells Fargo
- December 22 - John Obadiah Westwood, English entomologist
- December 23 - Joseph Smith, American religious leader, founder of The Church of Jesus Christ of Latter Day Saints Church and Latter Day Saint movement
- December 31 - Jeanne Deroin, French socialist and feminist
Undated
- Maiden of Ludmir, Jewish religious leader
- James Pratt, last of two men to be executed in UK for homosexuality
- Cochise, Indiginous American leader
Deaths
January–June
- January 7 - Ebenezer Sproat, American Continental Army officer, pioneer to the Ohio Country
- January 9 - Noble Wimberly Jones, American Continental Congressman
- January 17 - Paschen von Cossel, German lawyer
- January 18 - John Moore
- January 23 - Claude Chappe, French telecommunication pioneer
- February 2 - Thomas Banks, English sculptor and artist
- February 11 - Queen Jeongsun, Korean regent
- February 20 - Justus Claproth, German jurist, inventor of the de-inking process of recycled paper
- February 25 - Thomas Pownall, English colonial statesman
- March 4 - Jean-Baptiste Greuze, French painter
- May 7 - William Petty, 2nd Earl of Shelburne, Prime Minister of the United Kingdom
- May 9 - Friedrich Schiller, German playwright
- May 12 - Ferdinand von Hompesch zu Bolheim, 71st Grandmaster of the Order of Malta
- May 25
- * William Paley, English philosopher
- * Anna Maria Rückerschöld, Swedish author
- May 28 - Luigi Boccherini, Tuscan-born composer
- June 3 - Princess Louise of Saxe-Meiningen, Landgravine of Hesse-Philippsthal-Barchfeld
- June 18 - Arthur Murphy, Irish writer
- June 19 - Louis-Jean-François Lagrenée, French painter
July–December
- July 31 - Dheeran Chinnamalai, Tamil king
- August 3 - Christopher Anstey, English writer
- August 28
- * Alexander Carlyle, Scottish church leader
- * Christopher Gadsden, American statesman
- September 27 - William Moultrie, American general
- October 5
- * Charles Cornwallis, 1st Marquess Cornwallis, British general
- * Eleonore Prochaska, German heroine soldier
- October 21 - Horatio Nelson, British admiral
- November 24 - Jacques Antoine Marie de Cazalès, French orator, politician
- December 16 - Saverio Cassar, Gozitan priest, rebel leader
- December 23
- * Pehr Osbeck, Swedish explorer, naturalist
- * Geneviève Thiroux d'Arconville, French novelist, translator and chemist
Undated
- Rafaela Herrera, Nicaraguan heroine
- Bety of Betsimisaraka, queen regnant