1820 was a leap year starting on Saturday (see link for calendar).
Events
- January 1 - Constitutionalist military insurrection at Cádiz leads to summoning of Spanish parliament (March 7) and restoration of 1812 Constitution (March 8) by king Ferdinand VII. (See Mid-nineteenth century Spain.)
- January 28 - Russian expedition lead by Fabian Gottlieb von Bellingshausen and Mikhail Petrovich Lazarev approaches the Antarctic coast. (See History of Antarctica.)
- January 29 - George IV of the United Kingdom ascends the Throne, ending the period known as the English Regency.
- January 30 - Edward Bransfield lands on the Antarctic mainland. (See History of Antarctica.)
- February 6 - 86 free African American colonists sail from New York City to Freetown, Sierra Leone.
- February 23 - The Cato Street conspiracy is exposed. The principals are executed on May 1
- March 3 & 6 - Slavery in the United States: The Missouri Compromise becomes law.
- March 15 - Maine is admitted as the 23rd U.S. state.
- April - Radical War in Scotland
- May 1 - Last hanging drawing and quartering in Britain – Cato Street conspirators for treason (only hanged and beheaded) (See Capital punishment in the United Kingdom.)
- Spring - Joseph Smith, Jr. at age 14 claims to be visited in a vision by God and Jesus (Tradition holds that this occurred on April 6)
- July - Constitutionalist revolution in the Kingdom of the Two Sicilies
- August 24 - Constitutionalist insurrection at Oporto, Portugal; revolution in Lisbon, September 15 (See Portugal's crises of the Nineteenth Century.)
- October 9 - Guayaquil declare independence from Spain. (See also History of Ecuador).
- October 25-November 20 - Congress of Troppau (Opava) between rulers of Russia, Austria and Prussia
- November - U.S. presidential election: James Monroe is re-elected, virtually unopposed.
Unknown date
- The 6th Edition of Encyclopædia Britannica begins appearing.
- Republic of Buenos Aires (Argentina) establishes a penal colony in Falkland Islands.
- Venus de Milo found on the island of Melos.
- Hans Christian Ørsted discovers the relationship between electricity and magnetism.
Births
- January 17 - Anne Brontë, English author (d. 1849)
- February 8 - William Tecumseh Sherman, American Civil War general (d. 1891)
- February 15 - Susan B. Anthony, American suffragist (d. 1906)
- February 17 - Henri Vieuxtemps, Belgian composer (d. 1881)
- February 28 - John Tenniel, English illustrator (d. 1914)
- March 3 - Henry D. Cogswell, American philanthropist and temperance movement pioneer (d. ?).
- March 14 - Victor Emmanuel II of Italy (d. 1878)
- May 12 - Florence Nightingale, English nurse (d. 1910)
- May 27 - Mathilde Bonaparte, Italian princess (d. 1904)
- July 23 - Julia Gardiner Tyler, First Lady of the United States (d. 1889)
- September 17 - Émile Augier, French dramatist (d. 1889)
- September 27 - Wilhelm Siegmund Teuffel, German classical scholar (d. 1878)
- September 29 - Comte de Chambord, claimant to the French throne (d. 1883)
- October 6 - Jenny Lind, Swedish soprano (d. 1887)
- November 23 - Isaac Todhunter, English mathematician (d. 1884)
- November 28 - Friedrich Engels, German social philosopher (d. 1895)
- Harriet Tubman, American abolitionist activist (d. 1913)
Deaths
- January 29 - King George III of the United Kingdom (b. 1738)
- February 14 - Charles Ferdinand, Duke of Berry (stabbed) (b. 1778)
- March 22 - Stephen Decatur, American sailor (b. 1779)
- June 19 - Sir Joseph Banks, British naturalist and botanist (b. 1743)
- September 3 - Benjamin Latrobe, English architect (b. 1764)
- October 15 - Karl Philipp Fürst zu Schwarzenberg, Austrian field marshal (b. 1771)
- December 25 - Joseph Fouché, French statesman (b. 1763)