1864

January–March

 * January 16 – Denmark rejects a Prussian–Austrian ultimatum to repeal the Danish Constitution, which says that Schleswig-Holstein is part of Denmark.
 * January 21 – New Zealand Wars: The Tauranga Campaign starts.
 * February – John Wisden publishes The Cricketer's Almanack for the year 1864 in England; it will go on to become the major annual cricket reference publication.
 * February 1 – Danish-Prussian War (Second Schleswig War): 57,000 Austrian and Prussian troops cross the Eider River into Denmark.
 * February 17 – American Civil War: The tiny Confederate hand-propelled submarine H. L. Hunley sinks the USS Housatonic (1861) using a spar torpedo in Charleston Harbor, becoming the first submarine to sink an enemy ship, although the submarine and her crew of eight are also lost.
 * February 25 – American Civil War: The first Northern prisoners arrive at the Confederate prison at Andersonville, Georgia (the 500 prisoners had left Richmond, Virginia seven days before).
 * March 1 – Alejandro Mon y Menéndez takes office as Prime Minister of Spain.
 * March 9 – American Civil War: Abraham Lincoln appoints Ulysses S. Grant commander in chief of all Union armies.
 * March 10 – American Civil War: The Red River Campaign begins as Union troops reach Alexandria, Louisiana.
 * March 11 – Great Sheffield Flood: A reservoir near Sheffield, England bursts; 250 die.

April–June

 * April 12 – American Civil War: The Battle of Fort Pillow: Confederate forces kill most of the African American soldiers that surrendered at Fort Pillow, Tennessee.
 * April 15 – Choe Je-u, founder of the Donghak movement, is executed by beheading for sedition at Daegu in Korea.
 * April 18 – Danish-Prussian War (Second Schleswig War) – Battle of Dybbøl: The Prussian army fielding 10,000 men defeats the Danish defending army of 9,200 at Dybbøl Mill, after an artillery bombardment from April 7 to April 18.
 * April 22 – The United States Congress passes the Coinage Act of 1864 which mandates that the inscription "In God We Trust" be placed on all coins minted as United States currency.
 * May 2 – Under terms of the Treaty of London, the United Kingdom voluntarily cedes control of the United States of the Ionian Islands to the Kingdom of Greece.
 * May 5 – American Civil War: The Battle of the Wilderness begins in Spotsylvania County, Virginia.
 * May 7 – Clipper ship City of Adelaide launched in Sunderland, England. By the 21st century, she will be the world's oldest surviving clipper of only two survivors (Cutty Sark being the other).
 * May 7 – American Civil War: The Army of the Potomac, under General Ulysses S. Grant, breaks off from the Battle of the Wilderness and moves southwards.
 * May 8–21 – American Civil War – Battle of Spotsylvania Court House: Some 4,000 die in an inconclusive engagement.
 * May 9
 * Danish-Prussian War (Second Schleswig War) – Battle of Heligoland: the navy of Denmark and the allied navies of Austria and Prussia fight near the island of Heligoland with a tactical victory for Denmark. It is the last significant naval battle fought by squadrons of wooden ships and also the last involving Denmark.
 * American general John Sedgwick is shot dead during the Battle of Spotsylvania Court House shortly after uttering the famous last words: "They couldn't hit an elephant from this distance!"
 * May 11 – American Civil War – Battle of Yellow Tavern: Confederate General J. E. B. Stuart is mortally wounded at Yellow Tavern, Virginia.
 * May 12 – American Civil War – Battle of Spotsylvania Court House: The "Bloody Angle" – thousands of Union and Confederate soldiers die.
 * May 13 – American Civil War – Battle of Resaca: The battle begins with Union General Sherman fighting toward Atlanta.
 * May 15 – American Civil War – Battle of New Market: Cadets from the Virginia Military Institute fight alongside the Confederate Army to force Union General Franz Sigel out of the Shenandoah Valley.
 * May 18 – Civil War gold hoax: The New York World and the New York Journal of Commerce publish a fake proclamation that President Abraham Lincoln has issued a draft of 400,000 more soldiers.
 * May 20 – Australian bushranger Ben Hall and his gang escape from a shootout with police after attempting to rob the Bang Bang Hotel in Koorawatha, New South Wales.
 * May 20
 * American Civil War – Battle of Ware Bottom Church: In the Virginia Bermuda Hundred Campaign, 10,000 troops fight in this Confederate victory.
 * Death of John Clare, the Northamptonshire peasant poet (b. 1793) in Northampton General Lunatic Asylum, England.
 * May 21 – The Russian Empire begins the Ethnic cleansing of Circassians. More than 1.5 million Circassians are driven from their homeland to the Ottoman Empire, ending the Russo-Circassian War.
 * May 26 – Montana Territory is organized out of parts of Washington Territory and Dakota Territory, and is signed into law by President Abraham Lincoln.
 * June – United States Sanitary Commission's Sanitary Fair in Philadelphia takes place.
 * June 5 – American Civil War – Battle of Piedmont: Union forces under General David Hunter defeat a Confederate army at Piedmont, West Virginia, taking nearly 1,000 prisoners.
 * June 9 – American Civil War – Battle of Petersburg: Union forces under General Grant and troops led by Confederate General Robert E. Lee battle for the last time.
 * June 10 – American Civil War
 * Battle of Noonday Creek near Kennesaw, Georgia.
 * Battle of Brice's Crossroads: Confederate troops under Nathan Bedford Forrest defeat a much larger Union force led by General Samuel D. Sturgis in Mississippi.
 * June 12 – American Civil War – Battle of Cold Harbor: General Ulysses S. Grant pulls his troops from their positions at Cold Harbor, Virginia and moves south.
 * June 15 – Arlington National Cemetery is established in the United States when 200 acre of the grounds of Robert E. Lee's home Arlington House are officially set aside as a military cemetery by U.S. Secretary of War Edwin M. Stanton.
 * June 19 – American Civil War – Battle of Cherbourg: Confederate States Navy CSS Alabama is sunk in a single-ship action with USS Kearsarge in the English Channel off the coast of Cherbourg, France.
 * June 21 – New Zealand Wars: The Tauranga Campaign ends.
 * June 27 – American Civil War – Battle of Kennesaw Mountain near Kennesaw, Georgia.

July–September

 * July 4 – The University of Bucharest is founded.
 * July 18 – President Lincoln issues a true proclamation of conscription of 500,000 men for the U.S. Civil War.
 * July 19 – Third Battle of Nanking climaxes when the Taiping Heavenly Kingdom capital of Nanking falls to an assault by Imperial Qing dynasty forces in the last major action of the Taiping Rebellion in China. There are probably more than a million troops in the battle and the Taiping army sustains at least 100,000 dead.
 * July 20 – American Civil War – Battle of Peachtree Creek: Near Atlanta, Confederate forces led by General John Bell Hood unsuccessfully attack Union troops under General William T. Sherman.
 * July 22 – American Civil War – Battle of Atlanta: Outside of Atlanta, Confederate General Hood leads an unsuccessful attack on Union troops under General Sherman on Bald Hill.
 * July 24 – American Civil War – Second Battle of Kernstown: Confederate General Jubal Early defeats Union troops led by General George Crook in an effort to keep the Yankees out of the Shenandoah Valley.
 * July 28 – American Civil War – Battle of Ezra Church: Confederate troops led by General Hood make a third unsuccessful attempt to drive Union forces under General Sherman from Atlanta, Georgia.
 * July 29 – American Civil War: Confederate spy Belle Boyd is arrested by Union troops and detained at the Old Capitol Prison in Washington, D.C.
 * July 30 – American Civil War – Battle of the Crater: Union forces attempt to break Confederate lines by exploding a large bomb under their trenches.
 * August 1 – The Elgin Watch Company is founded in Elgin, Illinois.
 * August 5 – American Civil War – Battle of Mobile Bay: At Mobile Bay near Mobile, Alabama, Admiral David Farragut leads a Union flotilla through Confederate defenses and seals one of the last major Southern ports.
 * August 10 – An undeclared Uruguayan War begins when Uruguay refuses an ultimatum from the Empire of Brazil.
 * August 13 – The first fish and chips shop perhaps opens in London.
 * August 18 – American Civil War – Battle of Globe Tavern: Forces under Union General Ulysses S. Grant try to cut a vital Confederate supply-line into Petersburg, Virginia, by attacking the Wilmington and Weldon Railroad, forcing the Confederates to use wagons.
 * August 22 – First Geneva Convention for the Amelioration of the Condition of the Wounded in Armies in the Field is signed in Geneva by 12 European states under the auspices of the International Committee for Relief to the Wounded (predecessor of the International Red Cross and Red Crescent Movement).
 * August 31 – American Civil War: Union forces led by General William T. Sherman launch an assault on Atlanta.
 * September 1 – American Civil War: Confederate General Hood evacuates Atlanta after a 4-month siege mounted by Union General Sherman.
 * September 2 – American Civil War: Union forces under General Sherman enter Atlanta a day after the Confederate defenders fled the city.
 * September 5–6 – Bombardment of Shimonoseki: An American, British, Dutch and French alliance engages the powerful feudal Japanese warlord or daimyo Lord Mori Takachika of the Chōshū clan based in Shimonoseki, Japan.
 * September 7 – American Civil War: Atlanta, Georgia is evacuated on orders of Union General William Tecumseh Sherman.
 * September 8 – Delegates from the Canadian colonies meet at the Charlottetown Conference to discuss the Canadian Confederation.
 * September 16 – Pope Pius IX established the Diocese of Gozo.
 * September 17 – American Civil War Second Battle of Cabin Creek is fought in Indian Territory.
 * September 28 – The International Workingmen's Association is founded in London.

October–December

 * October 2 – American Civil War – First Battle of Saltville: Union forces attack Saltville, Virginia but are defeated by Confederate troops.
 * October 5 – A cyclone kills 70,000 in Calcutta, India.
 * October 9 – American Civil War – Battle of Tom's Brook: Union cavalrymen in the Shenandoah Valley defeat Confederate forces at Tom's Brook, Virginia.
 * October 12 – Uruguayan War: Forces of the Empire of Brazil invade Uruguay in support of Venancio Flores' Colorado Party.
 * October 28 – American Civil War – Second Battle of Fair Oaks: Union forces under General Ulysses S. Grant withdraw from Fair Oaks, Virginia, after failing to breach the Confederate defenses around Richmond, Virginia.
 * October 30
 * The Second Schleswig War is concluded. Denmark renounces all claim to Schleswig, Holstein, and Lauenburg, which come under Prussian and Austrian administration.
 * Helena, Montana, is founded after four prospectors (the so-called Four Georgians) discover gold at Last Chance Gulch; it is their last and agreed final attempt at weeks of trying to find gold in the northern Rockies.
 * October 31 – Nevada is admitted as the 36th U.S. state.
 * October 10 – Quebec Conference to discuss plans for the creation of a Dominion of Canada begins.
 * November 4 – American Civil War – Battle of Johnsonville: At Johnsonville, Tennessee, troops under the command of Confederate General Nathan Bedford Forrest bombard a Union supply base with artillery and destroy millions of dollars worth of material.
 * November 7 – The capital of Idaho Territory is moved from Lewiston to Boise; North Idaho declares the move illegal and proposes secession.
 * November 8 – U.S. presidential election, 1864: Abraham Lincoln is reelected in an overwhelming victory over George B. McClellan.
 * November 12 – Hostilities in the Paraguayan War open with the Paraguayan ship Tacuarí capturing the Brazilian Marquês de Olinda in the Paraguay River.
 * November 15 – American Civil War – Sherman's March to the Sea begins: Union General Sherman burns Atlanta and starts to move south, causing extensive devastation to crops and mills and living off the land.
 * November 20 – The judicial reform of Alexander II is launched in the Russian Empire.
 * November 22 – American Civil War – Sherman's March to the Sea: Confederate General John Bell Hood invades Tennessee in an unsuccessful attempt to draw Union General Sherman from Georgia.
 * November 25 – American Civil War: A group of Confederate operatives calling themselves the Confederate Army of Manhattan starts fires in more than 20 locations in an unsuccessful attempt to burn down New York City.
 * November 29 – American Indian Wars – Sand Creek massacre: Colorado volunteers led by Colonel John Chivington massacre at least 400 Cheyenne and Arapaho noncombatants at Sand Creek, Colorado (where they had been given permission to camp). Many of the dead are subsequently mutilated.
 * November 30 – American Civil War – Second Battle of Franklin: The Army of Tennessee led by General Hood mounts a dramatically unsuccessful frontal assault on Union positions around Franklin, Tennessee (Hood loses 6 generals and almost a third of his troops).
 * December 1 – Great Fire of Brisbane
 * December 4 – American Civil War – Sherman's March to the Sea: At Waynesboro, Georgia, forces under Union General Judson Kilpatrick prevent troops led by Confederate General Joseph Wheeler from interfering with Union General Sherman's campaign of destroying a wide swath of the South on his march to Savannah; Union forces suffer more than 3 times the casualties as the Confederates, however.
 * December 8
 * James Clerk Maxwell presents his paper A Dynamical Theory of the Electromagnetic Field to the Royal Society in London, treating light as an electromagnetic wave.
 * Syllabus errorum: Pope Pius IX condemns theological liberalism as an error and claims for the supremacy of Roman Catholic Church authority over the civil society. He also condemns rationalism and socialism.
 * The Clifton Suspension Bridge across the River Avon (Bristol) in England, designed by Isambard Kingdom Brunel and completed as a memorial to him, opens to traffic.
 * December 13 – Paraguayan War: Paraguay formally declares war on the Empire of Brazil in support of the Uruguayan National Party. The war continues to 1870 with around 300,000 Paraguayan deaths.
 * December 15–16 – American Civil War – Battle of Nashville: Union forces decisively defeat the Confederate Army of Tennessee.

Date unknown

 * The Dutch conquer southern Sumatra.
 * Ending of Second Anglo-Ashanti war.
 * Asa Shinn Mercer travels from Seattle to the U.S. East Coast and recruits 11 Mercer Girls, potential wives for men on the West Coast.
 * The first Quanjude Peking Roast Duck restaurant opens on Qianmen Street in Peking, China.

January–March

 * January 1
 * Alfred Stieglitz, American photographer (d. 1946)
 * Qi Baishi, Chinese painter (d. 1957)
 * January 8 – Prince Albert Victor, Duke of Clarence and Avondale (d. 1892)
 * January 9 – Alvah Curtis Roebuck, American Businessman (d. 1948)
 * January 10 – Annie Lowrie Alexander American physician and educator (d. 1929)
 * January 11 – Henry Marshall Tory, Canadian university founder (d. 1947)
 * January 13 – Wilhelm Wien, German physicist, Nobel Prize laureate (d. 1928)
 * January 21 – Israel Zangwill, British novelist and playwright (d. 1926)
 * January 24 – Marguerite Durand, French actress, journalist, and feminist leader (d. 1936)
 * January 26 – József Pusztai slovene writer, poet, journalist in Hungary (d. 1934)
 * January 28 – Herbert Akroyd Stuart, English mechanical engineer and inventor (d. 1927)
 * February 7 – Arthur Collins, American singer who recorded many early songs (d. 1933)
 * February 20 – Henry Rawlinson, 1st Baron Rawlinson, British general (d. 1925)
 * March 4 – David W. Taylor, U.S. Navy architect (d. 1940)
 * March 6 – Richard Rushall, British businessman (d. 1953)
 * March 12 – W. H. R. Rivers, English psychiatrist (d. 1922)
 * March 13 – Alexej von Jawlensky, Russian expressionist painter (d. 1941)
 * March 14 – Casey Jones, American railway engineer (d. 1900)
 * March 15 – Johan Halvorsen, Norwegian composer (d. 1935)
 * March 17 – Joseph Baptista, Indian Home Rule Movement founder (d. 1930)
 * March 19
 * Charles Marion Russell, American artist (d. 1926)
 * Mahatma Hansraj, Indian educationist, and Arya Samaj leader ( d. 1938)

April–June

 * April 6 – William Bate Hardy, English biologist and food scientist (d. 1934)
 * April 11 – Johanna Elberskirchen, German feminist (d. 1943)
 * April 12 – Rosslyn Wemyss, 1st Baron Wester Wemyss, British admiral (d. 1933)
 * April 21 – Max Weber, German sociologist (d. 1920)
 * May 4 – Marie Booth, the third daughter of William and Catherine Booth (d. 1937)
 * May 5 – Sir Henry Wilson, 1st Baronet, British field marshal and politician (d. 1922)
 * May 10 – Léon Gaumont, French film pioneer (d. 1946)
 * May 15 – Vilhelm Hammershøi, Danish painter (d. 1916)
 * June 2 – Wilhelm Souchon, German admiral (d. 1946)
 * June 3 – Ransom E. Olds, automotive pioneer (d. 1950)
 * June 10 – Ninian Comper, British architect (d. 1960)
 * June 11 – Richard Strauss, German composer (d. 1949)
 * June 13 – Dwight B. Waldo, American educator and historian (d. 1939)
 * June 14 – Alois Alzheimer, German psychiatrist and neuropathologist (d. 1915)
 * June 25 – Walther Nernst, German chemist, Nobel Prize laureate (d. 1941)
 * June 30 – Frederick Bligh Bond, English architect (d. 1945)

July–September

 * July 11 – Petar Danov, Bulgarian spiritual teacher (d. 1944)
 * July 12 – George Washington Carver, American botanist (d. 1943)
 * July 13 – John Jacob Astor IV, American businessman and inventor (d. 1912)
 * July 15 – Marie Tempest, English stage and film actress (d. 1942)
 * July 20
 * Erik Axel Karlfeldt, Swedish writer, Nobel Prize laureate (d. 1931)
 * Ruggero Oddi, Italian physiologist and anatomist (d. 1913)
 * July 21 – Frances Folsom Cleveland Preston, First Lady of the United States (d. 1947)
 * July 23 – Apolinario Mabini, Filipino political theoretician and Prime Minister (d. 1903)
 * August 9 – Roman Dmowski, Polish politician (d. 1939)
 * September 14 – Robert Cecil, 1st Viscount Cecil of Chelwood, English politician and diplomat, recipient of the Nobel Peace Prize (d. 1958)

October–December

 * October 5 – Louis Lumière, French inventor (d. 1948)
 * October 10 – T. Frank Appleby, United States Congressman from New Jersey (d. 1924)
 * October 25 – Alexander Gretchaninov, Russian composer (d. 1956)
 * October 31 – Cosmo Gordon Lang, Archbishop of Canterbury (d. 1945)
 * November 5 – Jessie Ralph, American actress (d. 1944)
 * November 1 – Grand Duchess Elizabeth Feodorovna of Russia (d. 1918)
 * November 11 – Alfred Hermann Fried, Austrian writer and pacifist, recipient of the Nobel Peace Prize (d. 1921)
 * November 13 – Bishop James Cannon Jr., American religious and temperance movement leader (d. 1944)
 * November 16 – Stéphane Javelle, French astronomer (d. 1917)
 * November 23 – Henry Bourne Joy, American business leader (d. 1936)
 * November 24 – Henri de Toulouse-Lautrec, French painter (d. 1901)
 * November 26 – Edward Higgins, 3rd General of The Salvation Army (d. 1947)
 * December 6
 * Alberico Albricci, Italian general (d. 1936)
 * William S. Hart, American film actor (d. 1946)
 * December 12 – Paul Elmer More, American critic and essayist (d. 1937)
 * December 23 – Princess Zorka of Montenegro (d. 1890)
 * December 25 – Thomas Cahill, American soccer coach (d. 1951)

January–June

 * January 13 – Stephen Foster, American composer (b. 1826)
 * January 27 – Leo von Klenze, German neoclassicist architect, painter and writer (b. 1784)
 * February 7 – Vuk Stefanović Karadžić, Serbian linguist and major reformer of the Serbian language (b. 1787)
 * February 22 – James Sewall Reed, US Army officer (in battle) (b.1832)
 * February 25 – Anna Harrison, First Lady of the United States (b.1775)
 * March 10 – King Maximilian II of Bavaria (b. 1811)
 * March 28 – Princess Louise Charlotte of Denmark (b. 1789)
 * April 4 – Joseph Pitty Couthouy, American naval officer (b. 1808)
 * April 14 – Charles Lot Church, Nova Scotia politician (b. 1777)
 * May 2 – Giacomo Meyerbeer, German composer (b. 1791)
 * May 5 – Elizabeth Andrew Warren, Cornish botanist and marine algolologist (b. 1786)
 * May 9 – John Sedgwick, Union general, American Civil War (b. 1813)
 * May 12 – J. E. B. Stuart, Confederate cavalry general, American Civil War (b. 1833)
 * May 19 – Nathaniel Hawthorne, American author (b. 1804)
 * June 1 – Hong Xiuquan, Chinese rebel (b. 1813)
 * June 13 – Henryk Dembiński, Polish engineer (b. 1791)
 * June 14 – Patrick Kelly, US Army officer (in battle) (b. ca. 1822)
 * June 15 – William E. Jones, Confederate general (in battle) (b. 1824)

July–December

 * August 3 – Jakob Walter, stonemason and common draftee (b. 1788)
 * August 4 – David Hansemann, Prussian politician (b. 1790)
 * August 19 – Trương Định, Vietnamese leader (suicide) (b. 1820)
 * September 3 – Emil Oskar Nobel, younger brother of Alfred Nobel (killed in an explosion) (b. 1843)
 * October 1 – Juan José Flores, former President of Ecuador (b. 1800)
 * October 12 – Roger Taney, United States Supreme Court Justice (b. 1777)
 * November 6 – Tuanku Imam Bonjol, Indonesian religious and military leader (b. 1772)
 * November 20 – Albert Newsam, American artist (b. 1809)
 * November 30
 * John Adams, Confederate Army officer (killed in action) (b. 1825)
 * Patrick Cleburne, Irish soldier and Confederate general (killed in action) (b. 1828)
 * December 1 – William L. Dayton – United States Minister to France (b. 1807)
 * December 8 – George Boole, English mathematician and philosopher (b. 1815)
 * December 21 – Archduke Louis of Austria (b. 1784)
 * December 23 – James Bronterre O'Brien, British Chartist (b. 1804)
 * December 24 – Mary Baker (née Willcocks) aka Princess Caraboo (b. 1791)
 * December 25 – Hank LaValle (b. 1845)
 * December 31 – George M. Dallas, U.S. Senator and 11th Vice President of the United States (b. 1792)