1821

January–March

June 24: Battle of Carabobo

• January 21 – Peter I Island in the Antarctic is first sighted, by Fabian Gottlieb von Bellingshausen.
• January 28 – Alexander Island, the largest in Antarctica, is first discovered by Fabian Gottlieb von Bellingshausen.
• February 9 – Columbian College of the District of Columbia is chartered by President Monroe.
• March 4 – James Monroe begins his second term as President of the United States.
• March 5 – President James Monroe is sworn in for his second term.
• March 25 (O.S.)/April 6 (N.S.) – Metropolitan bishop Germanos of Patras raises the revolutionary flag of Greece at the Monastery of Agia Lavra, symbolically marking the beginning of the Greek War of Independence against the Ottoman Empire; later celebrated as Greece's traditional Independence Day.

April–June

• April 10 – Ecumenical Patriarch Gregory V of Constantinople is blamed by the Ottoman government for being unable to suppress Greek independence, and is hanged outside the main gate of the Patriarchal Cathedral immediately after the celebration of Easter.
• May 5 – Emperor Napoleon dies in exile on Saint Helena of stomach cancer.
• May 26 – The Peloponnesian Senate is established by the Greek rebels.
• June 14 – King Badi VII of Sennar surrenders his throne and realm to Ismail Pasha, general of the Ottoman Empire, ending the existence of that Sudanese kingdom.
• June 19 – Battle of Drăgășani, Wallachia: The Filiki Eteria are decisively defeated by the Ottomans.
• June 24 – Battle of Carabobo: Simón Bolívar wins Venezuela's independence from Spain.
• June 27 – The New Hampton School is founded in the United States state of New Hampshire.

July–September

Date	Events	Photos
Wednesday, July 4	Return of John VI from Brazil who approves on that day the Bases da Constituição
Sunday, July 10	The United States takes possession of its newly bought territory of Florida from Spain.
Thursday, July 19	George IV is crowned king of the United Kingdom of Great Britain and Ireland.
Saturday, July 28	Peru declares independence from Spain.
Tuesday, August 4	The Saturday Evening Post is published for the first time, as a weekly newspaper in the United States.
Friday, August 10	Missouri is admitted as the 24th U.S. state (see History of Missouri).
Sunday, August 19	Navarino massacre: Greek rebels massacre 3,000 inhabitants of the city of Navarino.
Tuesday, August 21	Jarvis Island is discovered in the Pacific by the crew of the Eliza Frances.
Friday, August 24	The Treaty of Córdoba is signed in Córdoba, Veracruz, Mexico, ratifying the Plan of Iguala of February 24 for Mexico's independence from Spain and, although not recognised by the latter, effectively concludes the Mexican War of Independence.
Tuesday, September 4	Chilean general José Miguel Carrera is executed by an Argentinian military tribunal, in the city of Mendoza. Ukase of 1821: Russia proclaims territorial sovereignty over Northwestern North America, modern-day Alaska.
Friday, September 7	The Republic of Gran Colombia (a federation covering much of present-day Venezuela, Colombia, Panama, and Ecuador) is established, with Simón Bolívar as the founding President, and Francisco de Paula Santander as vice president.
Saturday, September 15	Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica gain independence from Spain by the Act of Independence of Central America. On October 29, the newly independent First Mexican Empire proposes that Guatemala should merge with it.
Tuesday, September 18	Amherst College is founded in Massachusetts.
Sunday, September 23	Greek War of Independence: The Siege of Tripolitsa ends, when Greek rebels capture the city of Tripoli, Greece.
Thursday, September 27	The Army of the Three Guarantees enters Mexico City, and the following day the Declaration of Independence of the Mexican Empire from Spain is proclaimed, following the Mexican War of Independence.

October–December

• October 5 – The massacre of 8,000 civilians follows the end of the Siege of Tripolitsa (Greek forces under the command of General Theodoros Kolokotronis had besieged the city for several months, during the Greek War of Independence from Turkey and the Ottoman Empire. ^{[1] [2]}
• October 8 – Tsar Alexander I of Russia issues an imperial ukase, guaranteeing freedom of commerce in Russia by merchants from Persia. ^[3]
• November 16 – American Old West: The Santa Fe Trail is first used by William Becknell.
• November 28 – Panama declares independence from Spain, joining Gran Colombia.
• December 1 – The Dominican Republic declares independence from Spain (see History of the Dominican Republic). It would be invaded by Haiti in 1822.
• December 6 – The South Orkney Islands are discovered, by George Powell and Nathaniel Palmer.^[4][5]
• December 15 – The world's first geographical society, the Société de géographie, is established in Paris.
• December 19 – The Eyjafjallajökull volcano in Iceland begins to erupt.

Date unknown

• The town of Al-Ubayyid, Sudan is established.
• High-quality cotton is introduced in Egypt.

January–June

James Longstreet

John C. Breckinridge

• January 2 – Catherine Huggins, British actor, singer, director and manager (d. 1887)
• January 8
  • James Longstreet, American Confederate general (d. 1904)
  • W. H. L. Wallace, American Civil War general (d. 1862)
• January 16 – John C. Breckinridge, the 14th Vice President of the United States (1857-1861) and Confederate Secretary of State in 1865 (d. 1875)
• February 3 – Elizabeth Blackwell, first American female physician (d. 1910)
• February 11
  • Hermann Allmers, German writer (d. 1902)
  • Auguste Edouard Mariette, French Egyptologist (d. 1881)
• February 17 – Lola Montez, Irish-Spanish dancer, royal mistress (d. 1861)
• February 19
  • Francis Preston Blair Jr., American politician, American Civil War officer (d. 1875)
  • August Schleicher, German linguist (d. 1868)
• February 22 – Athalia Schwartz, Danish writer, journalist and educator (d. 1871)
• March 1 – Joseph Hubert Reinkens, German Old Catholic bishop (d. 1896)
• March 9 – John Watts de Peyster, American author, philanthropist, and soldier (d. 1907)
• March 12 – Sir John Abbott, 3rd Prime Minister of Canada (d. 1893)
• March 15 – William Milligan, Scottish theologian (d. 1892)
• March 31 – Henry Dunning Macleod, Scottish economist (d. 1902)
• April 1 – Princess Anka Obrenović, Serbian princess (d. 1868)
• April 3 – Fr. Thomas Pelham Dale English mystic (d. 1892)
• April 9 – Charles Baudelaire, French poet, writer (d. 1867)
• May 6
  • Edmund Colhoun, American admiral (d. 1897)
  • Emilie Hammarskjöld, Swedish-American musician (d. 1854)
• May 8 – William Henry Vanderbilt, American entrepreneur (d. 1885)
• May 16 – Pafnuty Chebyshev, Russian mathematician (d. 1894)
• May 17 – Sebastian Kneipp, German naturopath (d. 1897)
• June 2 – Ion C. Brătianu, 2-Time Prime Minister of Romania (d. 1891)
• June 16 – Old Tom Morris, Scottish golfer (d. 1908)
• June 26 – Bartolomé Mitre, Argentine statesman, military figure, and author, 6th President of Argentina (d. 1906)

July–December

Louis Vuitton

Rudolf Virchow

Fyodor Dostoyevsky

• July 1 – Anatole Jean-Baptiste Antoine de Barthélemy, French archaeologist (d. 1904)
• July 2 – Charles Tupper, 6th Prime Minister of Canada (d. 1915)
• July 9
  • George Cavendish-Bentinck, British Conservative politician (d. 1891)
  • Adolphus Frederick Alexander Woodford, British parson (d. 1887)
• July 13 – Nathan Bedford Forrest, American Confederate Civil War General, first Grand Wizard of the Ku Klux Klan (d. 1877)
• July 16 – Mary Baker Eddy, American founder of Christian Science (d. 1910)
• July 17 – Friedrich Engelhorn, German industrialist and founder of BASF (d. 1902)
• July 18 – Pauline Viardot, French mezzo-soprano, composer (d. 1910)
• July 24 – William Poole, infamous member of New York City's Bowery Boys gang (d. 1855)
• July 27 – George H. Cooper, United States Navy admiral (d. 1891)
• August 10 – Jay Cooke, American financier (d. 1905)
• August 16 – Arthur Cayley, English mathematician (d. 1895)
• August 21 – Louis Vuitton, French fashion designer (d. 1892)
• August 31 – Hermann von Helmholtz, German physician and physicist (d. 1894)
• September 21 – Andrei Alexandrovich Popov, Russian admiral (d. 1898)
• September 28 – Jonathan Clarkson Gibbs, African-American minister, politician (d. 1874)
• October 13 – Rudolf Virchow, German physician, pathologist, biologist, and politician (d. 1902)
• October 20 – Eufrosina Popescu, Romanian actress (d. 1900)
• November 11 – Fyodor Dostoyevsky, Russian writer (d. 1881)
• November 30 – Frederick Temple, Archbishop of Canterbury (d. 1902)
• December 1 – John M. B. Clitz, American admiral (d. 1897)
• December 12 – Gustave Flaubert, French writer (d. 1880)
• December 22 – Junius Brutus Booth, Jr., American actor, theatre manager (d. 1883)
• December 24 – Gabriel García Moreno, former President of Ecuador (d. 1875)
• December 25 – Clara Barton, first president of American Red Cross (d. 1912)

Date unknown

• Giuseppe Bonavia, Maltese architect (d. 1885)

January–June

Napoleon Bonaparte

• January 4 – Elizabeth Ann Seton, American saint (b. 1774)
• January 5 – Carlo Porta, Milanese poet (b. 1775)
• January 19 – Alexandru Suţu, prince of Moldavia (b. 1758)
• February 23 – John Keats, British poet (b. 1795)^[6]
• March 4 – Princess Elizabeth of Clarence, daughter of William, Duke of Clarence (later King William IV) (b. 1820)
• March 13 – John Hunter, second Governor of New South Wales (b. 1737)
• April 10 – Patriarch Gregory V of Constantinople (b. 1746)
• April 20– Franz Karl Achard, German chemist, physicist and biologist (b. 1753)
• May 5 – Emperor Napoleon Bonaparte (I) of France (b. 1769)
• May 19 – Camille Jordan, French politician (b. 1771)
• June 7 – Tudor Vladimirescu, Wallachian rebel leader (b. c. 1780)
• June 17 – Martín Miguel de Güemes, Argentine military leader (b. 1785)
• June 30 – José Fernando de Abascal y Sousa, viceroy of Peru (b. 1743)

July–December

John William Polidori

• July 4 – Richard Cosway, English artist (b. 1742)
• August – Dorothea von Medem, Latvian diploma, duchess of Courland (b. 1761)
• August 24 – John William Polidori, English physician, writer (b. 1795) (suicide)
• September 4 – José Miguel Carrera, Chilean general, founding father (b. 1785)
• September 10 – Johann Dominicus Fiorillo, German painter, art historian (b. 1748)
• September 14 – Heinrich Kuhl, German naturalist, zoologist (b. 1797)
• October 4 – Marie-Louise Lachapelle, French obstetrician (b. 1769)
• October 8 – Juan O'Donojú, viceroy of New Spain (b. 1762)
• October 11 – John Ross Key, commissioned officer in the American Continental Army, judge, lawyer, father of songwriter Francis Scott Key (b. 1754)
• October 21 – Dorothea Ackermann, German actress (b. 1752)
• November 8 – Jean Rapp, French general (b. 1771)
• December 7 – King Pōmare II of Tahiti (b. 1782)
• December 12 – Phoebe Hessel, British female soldier (b. 1713)