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.

• January 16 – American Revolutionary War: Battle of Cape St. Vincent
• February – Armed Neutrality of the North alliance formed between Denmark, Sweden, and Russia.
• March 26 – The British Gazette and Sunday Monitor, the first Sunday newspaper in Britain
• 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 29 – American Revolutionary War: Loyalist forces under Col. Banastre Tarleton kill surrendering American soldiers in the Waxhaw Massacre.
• August 16 – American Revolutionary War: Battle of Camden – The British defeat the Americans near Camden, South Carolina.
• September 25 – Benedict Arnold flees to British-held New York
• October 2 – American Revolutionary War: British spy John Andre is hanged by American forces.
• October 10-16 – Great hurricane flattens the islands of Barbados, Martinique and St. Eustatius
• 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.

• Britain attacks the United Provinces before it can join the Neutral Alliance, because of its support for the American uprising.
• First Epsom Derby horse race run at Epsom Downs, Surrey, England.
• Emperor Kokaku ascends to the throne of Japan
• In Ireland, Lady Berry, who is sentenced to death for the murder of her son, is released when she agrees to become an executioner (retires 1810)
• Good grain and wine harvest in France
• 35th and last volume of Diderot's Encyclopédie published

for more information, see Category:1780 births.

for more information, see Category:1780 deaths.