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1780was 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.
- 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