Events of 1778

January–June

June 28: The Battle of Monmouth.

• January 18 – The third Pacific expedition of Capt. James Cook, with ships HMS Resolution and HMS Discovery, first view O'ahu then Kaua'i in the Hawaiian Islands, which he names the Sandwich Islands"'.

• February 5 – South Carolina becomes the first state to ratify the Articles of Confederation.

• February 6 – American Revolutionary War: In Paris the Treaty of Alliance and the Treaty of Amity and Commerce are signed by the United States and France, signaling official recognition of the new republic.

• February 23 – American Revolutionary War: Friedrich Wilhelm von Steuben arrives at Valley Forge, Pennsylvania and begins to train the American troops.

• March 10 – American Revolutionary War: George Washington approves the dishonorable discharge of Lieut. Frederick Gotthold Enslin for "attempting to commit sodomy, with John Monhort a soldier".

• May 30 – Benedict Arnold signs US oath of allegiance at Valley Forge

• June 24 – A total solar eclipse takes place across parts of USA from Texas to Virginia.

• June 28 – American Revolutionary War – Battle of Monmouth: George Washington's Continental Army battles the British general Sir Henry Clinton's army to a draw near Monmouth, New Jersey.

July–December

• July 3 – American Revolutionary War: the Wyoming Massacre takes place near Wilkes-Barre, Pennsylvania, ending in a terrible defeat of the local colonists.

• July 4 – American Revolutionary War: George Rogers Clark takes Kaskaskia.

• July 10 – Louis XVI of France declares war on the Kingdom of Great Britain.

• July 27 – American Revolution – First Battle of Ushant: British and French fleets fight to a standoff.

• August 26 – Triglav, at 2,864 meters above sea level the highest peak of Slovenia, is ascended for the first time by four brave men: Luka Korošec, Matevž Kos, Štefan Rožič, and Lovrenc Willomitzer on Sigmund Zois' initiative.

• August 29 – American Revolutionary War: The Battle of Rhode Island takes place when the Continental Army attempts to retake Aquidneck Island from the British.

• September – The Massachusetts Banishment Act, providing punishment for Loyalists, is passed.

• September 17 – The Treaty of Fort Pitt is signed, the first formal treaty between the United States and a Native American tribe (the Lenape or Delaware).

• September 19 – The Continental Congress passes the first budget of the United States.

• November 26 – In the Hawaiian Islands, Capt. James Cook becomes the first European to land on Maui.

November 26: Captain Cook lands on Maui.

Undated

• The first settlement is made in the area of what is now Louisville, Kentucky by 13 families under Colonel George Rogers Clark.

• Phillips Academy, the most prestigious secondary boarding school in the United States, is founded by Samuel Phillips Jr.

• First Ironbridge.

• The term "thoroughbred" is first used in the United States in an advertisement in a Kentucky gazette to describe a New Jersey stallion called Pilgarlick.

Births

• January 3 – Antoni Melchior Fijałkowski, Polish bishop (d. 1861)

• February 22 – Rembrandt Peale, American artist (d. 1860)

• March 19 – Edward Pakenham, British general (d. 1815)

• April 10 – William Hazlitt, English essayist (d. 1830)

• May 18 – Charles Vane, 3rd Marquess of Londonderry, British politician (d. 1854)

• August 11 – Friedrich Ludwig Jahn, German patriot (d. 1852)

• September 8 – Clemens Brentano, German poet (d. 1842)

• September 19 – Henry Peter Brougham, Lord Chancellor of Great Britain (d. 1868)

• November 1 – Gustav IV Adolf of Sweden (d. 1837)

• November 25 – Mary Anne Schimmelpenninck, British Christian writer (d. 1856)

• December 17 – Sir Humphry Davy, English chemist (d. 1829)

• December 19 – Marie Thérèse Charlotte (d. 1851)

• December 28 – Franciszek Ksawery Drucki-Lubecki, Polish politician (d. 1846)

• Sardar Fath `Ali Khan, Wazir-i-azam of Kabul (d. 1818)

Deaths

• January 10 – Carl Linnaeus, Swedish botanist (b. 1707)

• February 18 – Joseph Marie Terray, French statesman (b. 1715)

• February 20 – Laura Bassi, Italian scholar (b. 1711)

• March 5 – Thomas Arne, English composer of Rule, Britannia! (b. 1710)

• March 7 – Charles De Geer, Swedish industrialist and entomologist (b. 1720)

• March 13 – Charles le Beau, French historian (b. 1701)

• April 22 – James Hargreaves, English weaver, carpenter, and inventor (b. 1720)

• May 11 – William Pitt, 1st Earl of Chatham, Prime Minister of the United Kingdom (b. 1708)

• May 16 – Robert Darcy, 4th Earl of Holderness, English diplomat and politician (b. 1718)

• May 30 – Voltaire, French philosopher (b. 1694)

• June 12 – Philip Livingston, American signer of the Declaration of Independence (b. 1716)

• June 16 – Konrad Ekhof, German actor (b. 1720)

• June 24 – Pieter Burman the Younger, Dutch philologist (b. 1714)

• July 2 – Jean-Jacques Rousseau, Swiss philosopher (b. 1712)

• July 2 – Bathsheba Spooner, American murderer (b. 1746?)

• July 5 – James Townley, English dramatist (b. 1714)

• August 5 – Charles Clémencet, French historian (b. 1703)

• August 12 – Peregrine Bertie, 3rd Duke of Ancaster and Kesteven, British general and politician (b. 1714)

• November 9 – Giovanni Battista Piranesi, Italian artist (b. 1720)

• November 20 – Francesco Cetti, Italian Jesuit scientist (b. 1726)

• date unknown'' – Thomas Johnson, furniture maker (b. 1714)