| January 3 | Danish national anthem "Kong Kristian...," 1st sung |
| January 4 | Snowstorm hit Washington's army at Morristown, NJ |
| January 15 | Continental Congress establishes court of appeals |
| January 16 | Battle at Cape St. Vincent: Admiral Rodney beats Spanish fleet |
| March 1 | Pennsylvania becomes 1st U.S. state to abolish slavery (for new-borns only) |
| March 26 | 1st British Sunday newspaper appears (British Gazette and Sunday Monitor) |
| May 2 | William Herschel discovers 1st binary star, Xi Ursae Majoris |
| May 4 | American Academy of Arts and Science founded |
| May 4 | Charles Bunbury on Diomed wins 1st Epsom Derby |
| May 5 | 2nd oldest learned society in U.S. (American Academy of Arts and Sciences) forms (Boston) |
| May 12 | British troops occupy Charleston, South Carolina |
| May 12 | Charleston, South Carolina falls to British (Revolutionary War) |
| May 19 | About midday, near-total darkness descends on much of New England to this day it's cause is still unexplained |
| June 2 | Anti Catholic demonstration attacks parliament in London |
| June 7 | Anti-Catholic riot in London, 100s die |
| July 9 | Denmark declares neutrality |
| August 1 | Sweden declares neutrality |
| August 11 | Barbados hurricane begins |
| August 16 | British decisively defeat Americans in Battle of Camden, SC |
| August 22 | Resolution, without Captain Cook, returns to England |
| September 21 | Benedict Arnold gives British Major Andre plans to West Point |
| September 23 | British Major John Andre reveals Benedict Arnold's plot to betray West Pt |
| September 25 | Benedict Arnold joins the British |
| October 7 | British defeated by American militia near Kings Mountain, SC |
| October 10 | Great Hurricane of 1780 kills 20,000 to 30,000 in Caribbean |
| November 20 | Britain declares war on Holland |
| December 20 | England declares war on Netherlands |
