|Centuries:||17th century – 18th century – 19th century|
|Decades:||1750s 1760s 1770s – 1780s – 1790s 1800s 1810s|
|Years:||1781 1782 1783 – 1784 – 1785 1786 1787|
|1784 by topic:|
|Arts and Sciences|
|Archaeology – Architecture – Art – Literature (Poetry) – Music – Science|
|Canada –Denmark – France – Great Britain – Ireland – Norway – Russia – Scotland –Sweden – United States|
|Lists of leaders|
|Colonial governors – State leaders|
|Birth and death categories|
|Births – Deaths|
|Establishments and disestablishments categories|
|Establishments – Disestablishments|
|Ab urbe condita||2537|
|British Regnal year||24 Geo. 3 – 25 Geo. 3|
|Chinese calendar||癸卯年 (Water Rabbit)
4480 or 4420
— to —
甲辰年 (Wood Dragon)
4481 or 4421
|- Vikram Samvat||1840–1841|
|- Shaka Samvat||1706–1707|
|- Kali Yuga||4885–4886|
|Japanese calendar||Tenmei 4
|Julian calendar||Gregorian minus 11 days|
|Minguo calendar||128 before ROC
|Thai solar calendar||2326–2327|
|Wikimedia Commons has media related to 1784.|
1784 (MDCCLXXXIV) was a leap year starting on Thursday (dominical letter DC) of the Gregorian calendar and a leap year starting on Monday (dominical letter GF) of the Julian calendar, the 1784th year of the Common Era (CE) and Anno Domini (AD) designations, the 784th year of the 2nd millennium, the 84th year of the 18th century, and the 5th year of the 1780s decade. As of the start of 1784, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1918.
- January 6 – The Ottoman Empire agree to Russia's annexation of the Crimea in the Treaty of Constantinople.
- January 14 – The Congress of the United States ratifies the Treaty of Paris with Great Britain to end the American Revolutionary War, with the signature of President of Congress Thomas Mifflin.
- January 15 – Henry Cavendish's paper to the Royal Society of London, Experiments on Air, reveals the composition of water.
- February 28 – John Wesley ordains ministers for the Methodist Church in the United States.
- May 20 – A treaty is signed in Paris between the Kingdom of Great Britain and the Dutch Republic formally ending the Fourth Anglo-Dutch War.
- June 4 – Elizabeth Thible is the first woman to ride in a hot air balloon, at Lyon, France.
- August 15 – Cardinal de Rohan is called before the French court to account for his actions in the Affair of the Diamond Necklace.
- August 16 – Britain creates the colony of New Brunswick.
- September 22 – Russia establishes a colony at Kodiak, Alaska.
- October 31–December 14 – Revolt of Horea, Cloșca and Crișan in Transylvania, in consequence of which Joseph II, Holy Roman Emperor suspends the Hungarian Constitution.
- November 26 – The Roman Catholic Apostolic Prefecture of the United States is established.
- November 27 – The phenomenon of black holes is first posited in a paper by John Michell in the Philosophical Transactions of the Royal Society of London.
- December – Immanuel Kant's essay "Answering the Question: What Is Enlightenment?" is published.
- December 25 – The Methodist Episcopal Church in the United States is officially formed at the "Christmas Conference" led by Thomas Coke and Francis Asbury.
- The India Act requires that the governor general be chosen from outside the British East India Company and it makes company directors subject to parliamentary supervision.
- Britain receives its first bales of imported American cotton.
- King Carlos III of the Spanish Empire authorizes land grants in Alta California.
- Princess Yekaterina Vorontsova-Dashkova is named first president of the newly created Russian Academy.
- The North Carolina General Assembly incorporates the town of Morgansborough, named for Daniel Morgan. The town is designated as the county seat for Burke County, North Carolina and is subsequently renamed "Morgantown" and later shortened to become Morganton.
- The North Carolina General Assembly changes the name of Kingston, North Carolina, originally named for King George III of Great Britain, to Kinston.
- The Japanese famine continues as 300,000 die of starvation.
- A huge locust swarm hits South Africa.
- Benjamin Franklin invents bifocal spectacles.
- Benjamin Franklin tries in vain to persuade the French to alter their clocks in winter to take advantage of the daylight.
- Antoine Lavoisier pioneers quantitative chemistry.
- Cholesterol is isolated.
- Carl Friedrich Gauss pioneers the field of summation with the formula summing 1:n as (n(n+1))/2, at the age of 7.
- Madame du Coudray, pioneer of modern midwifery, retires.
- January 17 – Philippe Antoine d’Ornano, Marshal of France (d. 1863)
- January 28 – George Hamilton Gordon, 4th Earl of Aberdeen, Prime Minister of the United Kingdom (d. 1860)
- February 5 – Nancy Hanks, mother of Abraham Lincoln (d. 1818)
- February 29 – Leo von Klenze, German neoclassicist architect, painter and writer (d. 1864)
- April 5 – Louis Spohr, German violinist and composer (d. 1859)
- April 13 – Friedrich Graf von Wrangel, Prussian field marshal (d. 1877)
- June 24 – Juan Antonio Lavalleja, Uruguayan military and political figure (d. 1853))
- July 21 – Charles Baudin, French admiral (d. 1854)
- July 22 – Friedrich Bessel, German mathematician and astronomer (d. 1846)
- July 27 – Denis Davydov, Russian general and poet (d. 1839)
- September 4 – William Pope Duval, first civilian governor of Florida Territory (d. 1854)
- October 13 – King Ferdinand VII of Spain (d. 1833)
- October 15 – Thomas Robert Bugeaud, Marshal of France and duke of Isly (d. 1849)
- October 19
- October 20 – Henry Temple, 3rd Viscount Palmerston, Prime Minister of the United Kingdom (d. 1865)
- October – Sarah Biffen, armless English painter (d. 1850)
- November 24 – Zachary Taylor, 12th President of the United States (d. 1850)
- November 27 – August, Prince of Hohenlohe-Öhringen (d. 1853)
- February 27 – Count of St. Germain (b. 1710)
- April 26 – Nano Nagle, Irish convent founder (b. 1718)
- May 10 – Antoine Court de Gébelin, French pastor (b. 1725)
- May 12 – Abraham Trembley, Swiss naturalist (b. 1710)
- June 13 – Henry Middleton, American president of the Continental Congress (b. 1717)
- June 26 – Caesar Rodney, American lawyer and signer of the Declaration of Independence (b. 1728)
- July 1 – Wilhelm Friedemann Bach, German composer (b. 1710)
- July 31 – Denis Diderot, French philosopher and encyclopedist (b. 1713)
- August 4 – Giovanni Battista Martini, Italian musician (b. 1706)
- August 10 – Allan Ramsay, Scottish painter (b. 1713)
- August 14 – Nathaniel Hone, Irish-born painter (b. 1718)
- August 28 – Junípero Serra, Spanish Franciscan missionary (b. 1713)
- September 4 – César-François Cassini de Thury, French astronomer (b. 1714)
- September 8 – Ann Lee, American religious leader (b. 1736)
- December 5 – Phillis Wheatley, First African-American to publish a book (b. 1753)
- December 13 – Samuel Johnson, English writer and lexicographer (b. 1709)
- December 25 – Yosa Buson, Japanese poet and painter (b. 1716)
- December 26 – Seth Warner, American revolutionary leader (b. 1743)
- date unknown – Lê Quý Đôn, Vietnamese philosopher, poet, encyclopedist, and government official (b. 1726)
- Cavendish, Henry (1784). "Experiments on Air". Philosophical Transactions of the Royal Society of London. 75: 372–384. doi:10.1098/rstl.1785.0023. JSTOR 106582.
- Michell, John (1784). "On the Means of Discovering the Distance, Magnitude, &c. of the Fixed Stars, in Consequence of the Diminution of the Velocity of Their Light, in Case Such a Diminution Should be Found to Take Place in any of Them, and Such Other Data Should be Procured from Observations, as Would be Farther Necessary for That Purpose. By the Rev. John Michell, B.D.F.R.S. In a Letter to Henry Cavendish, Esq. F.R.S. and A.S.". Philosophical Transactions of the Royal Society of London. 75: 35–57. Bibcode:1784RSPT...74...35M. doi:10.1098/rstl.1784.0008. JSTOR 106576.