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1790 (MDCCXC) was a common year starting on Friday of the Gregorian calendar and a common year starting on Tuesday of the Julian calendar, the 1790th year of the Common Era (CE) and Anno Domini (AD) designations, the 790th year of the 2nd millennium, the 90th year of the 18th century, and the 1st year of the 1790s decade. As of the start of 1790, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923.
- January 8 – United States President George Washington gives the first State of the Union address, in New York City.
- January 11 – The 11 minor states of the Austrian Netherlands, which took part in the Brabant Revolution at the end of 1789, sign a Treaty of Union, creating the United States of Belgium. British Prime Minister William Pitt refuses to recognize the new confederation's independence.
- January 26 – Mozart's opera Così fan tutte premieres in Vienna.
- January 30 – The first boat specialized as a rescue lifeboat is tested on the River Tyne in England.
- February 1 – In New York City, the Supreme Court of the United States convenes for the first time.
- February 4 – Louis XVI of France declares to the National Assembly that he will maintain the constitutional laws.
- February 11 – Two Quaker delegates petition the United States Congress for the abolition of slavery.
- March 1 – The first United States Census is authorized; it is held later in the year.
- March 4 – France is divided into 83 départements, which cut across the former provinces, in an attempt to dislodge regional loyalties based on noble ownership of land.
- March 6 – The New York legislature consents to the admission to the Union of a new state, Vermont, formed within the boundaries of New York, contingent upon the successful conclusion of negotiations concerning disputed real-estate claims, and the boundary between the two states.
- March 21 – Thomas Jefferson reports to President George Washington in New York, as the new United States Secretary of State.
- July – Louis XVI of France accepts a constitutional monarchy.
- July 9 – Russo-Swedish War – Second Battle of Svensksund: In a massive Baltic Sea battle of 300 ships, the Swedish Navy captures one third of the Russian galley fleet: 304 Swedes are killed, 3,500 Russians killed and 6,000 captured, 51 Russian galleys and other rowing craft are sunk and 22 are taken.
- July 12 – French Revolution: The Civil Constitution of the Clergy is passed. This completes the destruction of the monastic orders, legislating out of existence all regular and secular chapters for either sex, abbacies and priorships.
- July 14 – French Revolution: Citizens of Paris celebrate the unity of the French people and the national reconciliation, in the Fête de la Fédération.
- July 16 – The signing of the Residence Bill establishes a site along the Potomac River as the District of Columbia, the capital district of the United States.
- July 26 – Alexander Hamilton's Assumption Bill, giving effect to his First Report on the Public Cr, is passed in the United States Congress, allowing the federal government to assume the consolidated debts of the U.S. states.
- July 27 – The Convention of Reichenbach is signed between Prussia and Austria.
- July 31 – Inventor Samuel Hopkins becomes the first to be issued a U.S. patent (for an improved method of making potash).
- August 4 – A newly passed U.S. tariff act creates the system of cutters for revenue enforcement (later named the United States Revenue Cutter Service), the forerunner of the Coast Guard.
- August 14 – The Treaty of Värälä ends the Russo-Swedish War.
- September 25 – The Peking Opera is born, when the Four Great Anhui Troupes introduce Anhui opera to Beijing, in honor of the Qianlong Emperor's 80th birthday.
- September 30 – Leopold II, Holy Roman Emperor starts to rule.
- October 7 – Commissioners appointed by the New York legislature announce the successful conclusion of negotiations between New York and Vermont, concerning disputed real-estate claims, and the consent of New York's legislature to the admission to the Union of the state of Vermont as the 14th State (which was formed within what New York claimed as its territory, under an Order in Council, that King George III issued on July 20, 1764).
- November – Holy Roman forces recapture the Austrian Netherlands.
- December 10 – The Hawkesbury and Nepean Wars begin in New South Wales, Australia, as a result of deterioration in relations and increasing colonization.
- December 11 – Russo-Turkish War (1787–92): During Alexander Suvorov's storm of Izmail, 26,000 Turkish soldiers lose their lives.
- January 5 – Melchor Múzquiz, 5th President of Mexico (d. 1844)
- January 18 – Qi Shan, Manchu Qing official (d. 1854)
- March 3 – John Austin, English jurist (d. 1859)
- March 29 – John Tyler, 10th President of the United States (d. 1862)
- April 21 – Manuel Blanco Encalada, Spanish-Chilean admiral and politician, 1st President of Chile (d. 1876)
- May 20 – Micajah Thomas Hawkins, American politician (d. 1858)
- May 23 – Jules Dumont d'Urville, French explorer (d. 1842)
- June 1 – Ferdinand Raimund, Austrian playwright (d. 1836)
- June 13 – José Antonio Páez, 19th President of Venezuela (d. 1873)
- June 24 – Helena Ekblom, Swedish preacher (d. 1859)
- September 6 – John Green Crosse, English surgeon (d. 1850)
- November 12 – Letitia Christian Tyler, First Lady of the United States (d. 1842)
- November 17 – August Ferdinand Möbius, German mathematician, astronomer (d. 1868)
- November 21 – Edmund Lyons, 1st Baron Lyons, British admiral (d. 1858)
- December 8
- December 16 – Léopold I of Belgium (d. 1865)
- December 19 – William Edward Parry, English Arctic explorer (d. 1855)
- December 23 – Jean-François Champollion, French Egyptologist (d. 1832)
- December 31 – Antonie Adamberger, Austrian stage actress (d. 1867)
- February 20 – Joseph II, Holy Roman Emperor (b. 1741)
- March 4 – Henry Wisner, American Continental Congressman for New York (b. 1720)
- March 12
- April 17 – Benjamin Franklin, American scientist, statesman (b. 1706)
- May 4 – Matthew Tilghman, American Continental Congressman for Maryland (b. 1718)
- May 9 – William Clingan, American Continental Congressman for Pennsylvania (b. c.1721)
- May 16 – Philip Yorke, 2nd Earl of Hardwicke, English politician (b. 1720)
- May 20 – Nathan Miller, American Continental Congressman for Rhode Island (b. 1743)
- May 21 – Thomas Warton, English poet (b. 1728)
- May 26 – Nathaniel Folsom, American Continental Congressman for New Hampshire and Revolutionary War major general (b. 1726)
- May 29 – Israel Putnam, American Revolutionary War general (b. 1718)
- June 1 – Theodorick Bland, American Continental Congressman and U.S. Representative for Virginia (b. 1741)
- June 25 – Lovisa Augusti, Swedish opera singer (b. 1756)
- July 3 – Jean-Baptiste L. Romé de l'Isle, French chemist (b. 1736)
- July 7 – François Hemsterhuis, Dutch philosopher (b. 1721)
- July 14 – Ernst Gideon von Laudon, Austrian field marshal (b. 1717)
- July 17 – Adam Smith, Scottish economist, philosopher (b. 1723)
- July 25
- August 16 – David Brearley, American Revolutionary War colonel, signer of the U.S. Constitution for New Jersey, and federal judge (b. 1745)
- September 2 – Johann Nikolaus von Hontheim, German historian, theologian (b. 1701)
- October 14 – William Hooper, American signer of the Declaration of Independence and Continental Congressman for North Carolina (b. 1742)
- October 19 – Lyman Hall, American signer of the Declaration of Independence and Governor of Georgia (1783-1784)(b. 1724)
- November 6 – James Bowdoin, American Governor of Massachusetts (b. 1726)
- November 16 – Daniel of St. Thomas Jenifer, American Continental Congressman and Signer of the U.S. Constitution for Maryland (b. 1723)
- November 27 – Robert Livingston, American member of the New York colonial assembly (1737-1758) (b. 1708)
- December 14 – John Hulse, English clergyman (b. 1708)
- December 16 – Benjamin Andrew, American Continental Congressman for Georgia and member of the Georgia House of Representatives (b. 1713)
- date unknown - Helen Gloag, Scottish slave, Empress of Morocco (b. 1750)