) was a leap year starting on Saturday
(link will display the full calendar) of the Gregorian calendar
(or a leap year starting on Wednesday
of the 11-day slower Julian calendar
Events of 1780
January - June
- January 16 - American Revolutionary War - Battle of Cape St. Vincent: British Admiral Sir George Rodney defeats a Spanish fleet.
- February - The League of Armed Neutrality is formed between Denmark, Sweden, and Russia.
- February 29 - The Omicron Delta Omega co-ed fraternity is founded by Benjamin Franklin.
- March 8 - Formation of the League of Armed Neutrality is soon followed by the start of the Fourth Anglo-Dutch War.
- March 26 - The British Gazette and Sunday Monitor, the first Sunday newspaper in Britain, begins publication.
- April 16 - The University of Münster in Münster, North Rhine-Westphalia, Germany is founded.
- May 12 - American Revolutionary War: Charleston, South Carolina is taken by British forces.
- May 19 - New England's Dark Day: An unaccountable darkness spreads over New England, regarded by some observers as a fulfillment of Bible prophecy.
- May 29 - American Revolutionary War: Loyalist forces under Col. Banastre Tarleton kill surrendering American soldiers in the Waxhaw Massacre.
- June 2 - Gordon Riots in London, Great Britain: The Duke of Richmond calls, in the House of Lords, for manhood suffrage and annual parliaments.
July - December
- February 14 - William Blackstone, English jurist (b. 1723)
- February 17 - Andreas Felix von Oefele, German historian and librarian (b. 1706)
- February 18 - Kristijonas Donelaitis, Lithuanian poet (b. 1714)
- March 26 - Charles I, Duke of Brunswick-Lüneburg (b. 1713)
- May 18 - Charles Hardy, British governor of Newfoundland (b. c. 1714)
- June 3 - Thomas Hutchinson, American colonial governor of Massachusetts (b. 1711)
- July 4 - Prince Charles Alexander of Lorraine, Austrian military leader (b. 1712)
- July 14 - Charles Batteux, French philosopher (b. 1713)
- August 3 - Étienne Bonnot de Condillac, French philosopher (b. 1715)
- August 29 - Jacques-Germain Soufflot, French architect (b. 1713)
- September 4 - John Fielding, English magistrate and social reformer (b. 1721)
- September 8 - Enoch Poor, American Revolutionary general (b. 1736)
- October 2 - John André, British Army officer of the American Revolutionary War (executed) (b. 1750)
- October 17 - William Cookworthy, English chemist (b. 1705)
- November 26 - Sir James Denham Steuart, 4th Baronet, British economist (b. 1712)
- November 29 - Empress Maria Theresa of Austria (b. 1717)
- December 26 - John Fothergill, English physician (b. 1712)
- date unknown - Thomas Dilworth, British cleric and writer