1820 (MDCCCXX, in Roman numerals) was a leap year of the 19th century of the current Gregorian Calendar, of the Age of Christ, and its dominical letters were B and A (52 weeks), it started on a Saturday and ended on a Sunday.
Joseph Smith Jr. had the First Vision
Foundation of the City of Port Elizabeth in South Africa.
Appointment of Francisco de Borja Garção Stockler appointed him as 8th captain general of the Azores.
Introduction of tobacco culture on the island of São Miguel, Azores.
Accession of the Azores Islands to the Liberal Revolution.
March 15 - Maine becomes the 23rd US state.
July 8 - D. João VI, through the Royal Charter, declared the Captaincy of Sergipe d'El Rei (current state of Sergipe) exempt from the subjection of the province of Bahia.
24th of August - the Liberal Revolution in Porto breaks out.
August 24 - The Provisional Board of the Supreme Government of the Kingdom is established in Porto, presided over by Brigadier António da Silveira Pinto da Fonseca, future Viscount of Canelas.
February 15 - Arvid Posse, prime minister of Sweden (d. 1901).
February 23 - Jakob Stämpfli, was President of the Swiss Confederation in 1856 (d. 1879).
March 2 - Multatuli, Dutch writer (d. 1887).
March 14 - Victor Emmanuel II, King of Italy.
March 30 - Anna Sewell, English writer. (d. 1878).
May 12 - Florence Nightingale, nurse (d. 1910).
July 5 – William Rankine, British physicist and engineer (d. 1872).
August 2 - Nord Alexis, president of Haiti from 1902 to 1908 (d. 1910).
October 16 - Gillis Bildt, Prime Minister of Sweden (d. 1894).
November 28 – Friedrich Engels, intellectual partner of Karl Marx (d. 1895).
January 14 - Wilhelmina Carolina of Denmark, elector-consort of Hesse (b. 1747).
June 20 - Manuel Belgrano, economist, politician, lawyer, Argentine military (b. 1770).
June 21 - Alexis Thérèse Petit, French physicist (b. 1791).
September 14 – François Joseph Lefebvre, Duke of Dánzig, Marshal of the First French Empire (b. 1755).
Tsulthrim Drayga, Desi Druk of the Kingdom of Bhutan (b. 1790).
January 29 – George III of the United Kingdom, King of the United Kingdom of Great Britain and Ireland (b. 1738)