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1780 (MDCCLXXX) was a leap year starting on Saturday of the Gregorian calendar and a leap year starting on Wednesday of the Julian calendar, the 1780th year of the Common Era (CE) and Anno Domini (AD) designations, the 780th year of the 2nd millennium, the 80th year of the 18th century, and the 1st year of the 1780s decade. As of the start of 1780, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923.
- October 2 – American Revolutionary War – In Tappan, New York, British spy John André is hanged by American forces.
- October 7 – American Revolutionary War – Battle of Kings Mountain: Patriot militia forces annihilate Loyalists under British Major Patrick Ferguson, at Kings Mountain, South Carolina.
- October 10–16 – The Great Hurricane flattens the islands of Barbados, Martinique and Sint Eustatius; 22,000 are killed.
- November 4 – Rebellion of Túpac Amaru II: In the Spanish Viceroyalty of Peru, Túpac Amaru II leads an uprising of Aymara and Quechua peoples and mestizo peasants as a protest against the Bourbon Reforms.
- November 28 – A lightning strike in Saint Petersburg begins a fire that burns 11,000 homes.
- November 29 – Maria Theresa of Austria dies, and her Habsburg dominions pass to her ambitious son, Joseph II, who has already been Holy Roman Emperor since 1765.
- November 30 – American Revolutionary War: The British San Juan Expedition is forced to withdraw.
- December 16 – Emperor Kōkaku accedes to the throne of Japan.
- December 20 – The Fourth Anglo-Dutch War begins.
- Jose Gabriel Kunturkanki, businessman and landowner, proclaims himself Inca Túpac Amaru II.
- The Duke of Richmond calls, in the House of Lords of Great Britain, for manhood suffrage and annual parliaments, which are rejected.
- Jeremy Bentham's Introduction to Principles of Morals and Legislation, presenting his formulation of utilitarian ethics, is printed (but not published) in London.
- Nikephoros Theotokis starts introducing Edinoverie, an attempt to integrate the Old Believers into Russia's established church.
- The Woodford Reserve bourbon whiskey distillery begins operation in Kentucky.
- In Ireland, Lady Berry, who is sentenced to death for the murder of her son, is released when she agrees to become an executioner (she retires in 1810).
- The original Craven Cottage is built by William Craven, 6th Baron Craven, in London, on what will become the centre circle of Fulham F.C.'s pitch.
- The amateur dramatic group Det Dramatiske Selskab is founded in Christiania, Norway.
- Western countries pay 16,000,000 ounces of silver for Chinese goods.
- The Kingdom of Great Britain reaches c.9 million population.
беларуская (тарашкевіца): 1780
srpskohrvatski / српскохрватски: 1780