Benito Juárez captures Mexico City.
First steam-powered carousel recorded, in Bolton, England.
January 2 – Friedrich Wilhelm IV of Prussia dies and is succeeded by Wilhelm I.
January 3 – American Civil War: Delaware votes not to secede from the Union.
January 9 – American Civil War: Mississippi becomes the second state to secede from the Union.
January 10 – American Civil War: Florida secedes from the Union.
January 11 – American Civil War: Alabama secedes from the Union.
January 12 – American Civil War: Major Robert Anderson sends dispatches to Washington.
January 19 – American Civil War: Georgia secedes from the Union.
January 21 – American Civil War: Jefferson Davis resigns from the United States Senate.
January 26 – American Civil War: Louisiana secedes from the Union.
January 29 – Kansas is admitted as the 34th U.S. state.
February 1 – American Civil War: Texas secedes from the Union.
February 4 – American Civil War: In Montgomery, Alabama, the Provisional Confederate States Congress is formed by representatives from the first seven break-away states.
February 8 – American Civil War: The Confederate States of America are formed, comprising the first seven break-away States.
February 9 – American Civil War: Jefferson Davis is elected the Provisional President of the Confederate States of America by the Weed Convention at Montgomery, Alabama.
American Civil War: The U.S. House unanimously passes a resolution guaranteeing non-interference with slavery in any state.
About 850 convicts at Chatham Dockyard in England take over their prison in a riot.
February 13 – Italian unification: The Siege of Gaeta, stronghold of the Neapolitan King Francis II, is ended by Piedmontese forces. Francis goes into exile.
February 18 – American Civil War: In Montgomery, Alabama, Jefferson Davis is inaugurated as the provisional president of the Confederate States of America.
February 20 – In Britain, storms damage the Crystal Palace and cause the collapse of the steeple of Chichester Cathedral.
February 23 – President-elect Abraham Lincoln arrives secretly in Washington, D.C. after an assassination attempt in Baltimore.
February 24 – Battle of Ky Hoa: the French and the Spanish defeat the Vietnamese.
February 27 – Russian troops fire upon a crowd in Warsaw protesting Russian rule over Poland, killing 5 protesters.
February 28 – Colorado is organized as a United States territory.
Nevada is organized as a United States territory.
American Civil War: Texas is admitted to the Confederate States of America.
March 3 (February 19 O.S.) – Emancipation reform of 1861: Serfdom is abolished in the Russian Empire.
Abraham Lincoln is sworn in as President of the United States.
American Civil War: The "Stars and Bars" is adopted as the flag of the Confederate States of America.
March 10 – El Hadj Umar Tall seizes the city of Ségou, destroying the Bamana Empire of Mali.
March 11 – American Civil War: The Constitution of the Confederate States of America is adopted.
March 13 – Tsushima incident: the Russian corvette Posadnik arrives at Tsushima Island in the Korea Strait, Japan, provoking a reaction from the Japanese Shogunate.
March 17 – Italian unification: The Kingdom of Italy is proclaimed by the new Parliament, with Victor Emmanuel II of Piedmont-Sardinia becoming its king.
March 19 – The First Taranaki War ends in New Zealand.
An earthquake completely destroys Mendoza, Argentina.
Italian unification: The surrender of Civitella del Tronto ends the Kingdom of the Two Sicilies.
March 21 – Alexander Stephens, Vice President of the Confederacy, gives the infamous Cornerstone Speech in Savannah, Georgia, in which he declares that slavery is the natural condition of blacks and the foundation of the Confederacy.
March 28 – Confederate Arizona: convention in present-day Tucson ratified the ordinance of secession of southern part of New Mexico Territory.
March 30 – Discovery of the chemical elements: Sir William Crookes announces his discovery of thallium.
April 7 – A population census is taken in the United Kingdom.
April 12 – The American Civil War begins with the bombardment of Fort Sumter, South Carolina.
April 13 – American Civil War: Fort Sumter surrenders to Southern forces.
April 15 – American Civil War: President Abraham Lincoln issues a Proclamation calling for 75,000 men to confront in the South, "combinations too powerful to be suppressed in the ordinary way".
April 17 – American Civil War: The state of Virginia secedes from the Union.
April 20 – American Civil War: Robert E. Lee resigns his commission in the United States Army in order to command the forces of the state of Virginia.
April 24 (N.S.) – Bezdna in Russia is the scene of a peasant uprising; the military open fire and nearly 5000 are killed.
April 25 – American Civil War: The Union Army arrives in Washington, D.C.
April 26 – Giovanni Schiaparelli discovers the asteroid 69 Hesperia.
April 27 – American Civil War:
President Abraham Lincoln suspends the writ of habeas corpus in the United States.
May 6 – American Civil War: Arkansas secedes from the Union.
May 7 – American Civil War: Tennessee secedes from the Union.
May 8 – American Civil War: Richmond, Virginia is named the capital of the Confederate States of America.
North Star Affair: The British merchant ship North Star leaves Hong Kong for Nagasaki, Japan. Chinese pirates board the vessel, kill an officer, and escape with a large quantity of gold.
American Civil War: Queen Victoria of the United Kingdom issues a "proclamation of neutrality" which recognizes the breakaway states as having belligerent rights.
Comet C/1861 J1 (the "Great Comet of 1861") is discovered in Australia.
May 14 – The Canellas meteorite, an 859 gram chondrite type meteorite, strikes Earth near Barcelona, Spain.
May 20 – American Civil War: Kentucky proclaims its neutrality which lasts until September 3, when Confederate forces enter the state. North Carolina secedes from the Union.
May 21 – Russian sailors clash with a group of Japanese samurai and farmers at Tsushima island.
May 23 – American Civil War: The state of Virginia's ordinance of secession from the United States is ratified in a referendum held on May 23, 1861.
May 29 – Establishment of Hong Kong General Chamber of Commerce
June 9 – The Règlement Organique: With the approval of European powers, the Mount Lebanon Mutasarrifate is established as a semi-autonomous sub-division separate from the Sidon Eyalet. An Ottoman Armenian, Davud Pasha, is appointed Mutasarrıf by the Ottoman Sultan.
June 15 – Benito Juárez is formally elected President of Mexico; he temporarily stops the payments of foreign debt.
June 22 – Tooley Street fire starts and takes the life of James Braidwood first director of the London Fire Brigade.
June 25 – Abdülmecid I, Sultan of the Ottoman Empire (1839–1861) dies and is succeeded by Abdülaziz (1861–1876).
The first issue of the Vatican's newspaper L'Osservatore Romano is published.
Taiping Rebellion: French and Imperial Chinese troops defeat Taiping forces at the Battle of Shanghai.
July 2 – Ivan Kasatkin lands on Hakodate and introduces the Eastern Orthodox Church into Japan.
July 12 – Confederate States signed Treaty with Choctaws and Chickasaws in Indian Territory.
July 13 – American Civil War: The Battle of Corrick's Ford takes place in western Virginia.
July 21 – American Civil War: First Battle of Bull Run: At Manassas Junction, Virginia, the first major battle of the war ends in a Confederate victory.
July 25 – American Civil War: The Crittenden–Johnson Resolution is passed by the U.S. Congress, stating that the war is being fought to preserve the Union and not to end slavery.
July 26 – American Civil War: George B. McClellan assumes command of the Army of the Potomac following the disastrous Union defeat at the First Battle of Bull Run.
American Civil War: In order to help pay for the war effort, the United States government issues the first income tax as part of the Revenue Act of 1861 (3% of all incomes over US$800; rescinded in 1872).
The U.S. Army abolishes flogging.
August 10 – American Civil War: The first major battle west of the Mississippi River, the Battle of Wilson's Creek, is fought, with a Confederate victory.
August 19 – First ascent of Weisshorn, fifth highest summit in the Alps.
August 27 – Martin Doyle's is the last execution in Britain for attempted murder.
September – The first complete identified remains of Archaeopteryx are discovered in Germany.
September 3 – American Civil War: Confederate General Leonidas Polk invades neutral Kentucky, prompting the state legislature to ask for Union assistance.
September 6 – American Civil War: Forces under Union General Ulysses S. Grant bloodlessly capture Paducah, Kentucky, which gives the Union control of the mouth of the Tennessee River.
October 9 – American Civil War: Battle of Santa Rosa Island – Confederate forces are defeated in their effort to take the island.
October 21 – American Civil War: Battle of Ball's Bluff – Union forces under Colonel Edward Baker are defeated by Confederate troops in the second major battle of the war. Baker, a close friend of Abraham Lincoln, is killed in the fighting.
October 24 – HMS Warrior, the world's first ocean-going (all) iron-hulled armored battleship, is completed and commissioned into the British Royal Navy.
October 25 – Toronto Stock Exchange established in Canada.
October 26 – The Pony Express announces its closure.
October 28 – American Civil War: The Missouri legislature takes up a bill for Missouri's secession from the Union.
October 30 – American Civil War: The bill for Missouri's secession from the Union is passed.
The Spanish, French and British governments sign a tripartite agreement to intervene in Mexico, in the hope of recovering unpaid debts.
The Missouri secession bill is signed by Governor Jackson.
American Civil War: Citing failing health, Union General Winfield Scott resigns as Commander of the United States Army.
November 1 – American Civil War: U.S. President Abraham Lincoln appoints George B. McClellan as commander of the Union Army, replacing the aged General Winfield Scott.
November 2 – American Civil War: Western Department Union General John C. Frémont is relieved of command and replaced by David Hunter.
November 6 – American Civil War: Jefferson Davis is elected president of the Confederate States of America.
November 5 – The first Melbourne Cup horse race is held in Melbourne, Australia.
November 7 – American Civil War: Battle of Belmont – In Belmont, Missouri, Union forces led by General Ulysses S. Grant overrun a Confederate camp but are forced to retreat when Confederate reinforcements arrive.
November 8 – American Civil War: Trent Affair – The USS San Jacinto stops the United Kingdom mail ship Trent and arrests two Confederate envoys, James Mason and John Slidell, sparking a diplomatic crisis between the U.K. and U.S..
November 10 – Following the death of Henri Mouhot, his servant Phrai begins shipping his diaries and specimens back to the west; they include accounts of Mouhot's discovery of Angkor Wat.
November 19 – American Civil War: Battle of Round Mountain in Indian Territory (present-day Oklahoma.
November 21 – American Civil War: Confederate President Jefferson Davis appoints Judah Benjamin Secretary of War.
November 25 – A tenement collapses in the Old Town, Edinburgh killing 35 with 15 survivors.
November 28 – Acting on the ordinance passed by the Jackson government, the Confederate Congress admits Missouri as the 12th Confederate state.
American Civil War: Kentucky is accepted into the Confederate States of America.
In southern French Indochina, resistance forces led by Nguyễn Trung Trực ambush, board and sink the French lorcha (boat) L'Esperance on the Nhat Tao canal.
The British Empire establishes bases in Lagos to stop the slave trade.
Perpetual Truce of Peace and Friendship signed between Bahrain and the United Kingdom.
First industrial meat packing plant in Uruguay established at Fray Bentos.
The Royal Seminary become the first public institution of higher academic learning open to women in Sweden.
January 6 – János Zsupánek, Slovene (Prekmurje Slovene) poet and writer (d. 1951)
January 14 – Mehmed VI, Ottoman Sultan (d. 1926)
January 28 – Julián Felipe, Filipino musician and bandleader (d. 1944)
January 30 – Charles Martin Loeffler, American composer (d. 1935)
February 12 – Lou Andreas-Salomé, Russian-born author (d. 1937)
February 15 – Charles Édouard Guillaume, French physicist, Nobel Prize laureate (d. 1938)
February 17 – Princess Helena, Duchess of Albany, (d. 1922)
February 19 – Henry Horne, 1st Baron Horne, British general (d. 1929)
February 26 – King Ferdinand of Bulgaria (d. 1948)
February 27 – Rudolf Steiner, Austrian philosopher, social reformer and author (d. 1925)
March 2 – Nikola Ivanov, Bulgarian general (d. 1940)
March 12 – József Konkolics, Hungarian Slovene writer (d. 1941)
April 2 – Iván Persa, Hungarian Slovene writer and Catholic priest (d. 1935)
April 6 – Stanislas de Guaita, French poet (d. 1897)
April 8 – Son Byong-hi, Korean independence activist (d. 1922)
April 15 – Bliss Carman, Canadian poet (d. 1929)
Edmund Allenby, 1st Viscount Allenby, British soldier and administrator (d. 1936)
John Peltz, professional baseball player (d. 1906)
April 24 – Hedda Andersson, Swedish physician (d. 1950)
May 5 – Peter Cooper Hewitt, American electrical engineer and inventor (d. 1921)
May 7 – Rabindranath Tagore, Indian writer, Nobel Prize laureate (d. 1941)
May 11 – Frederick Russell Burnham, American scouter(d. 1947)
May 14 – Harro Magnussen, German sculptor (d. 1908)
May 16 – Herman Webster Mudgett, alias H. H. Holmes, American serial killer (d. 1896)
May 24 – Gerald Strickland, 4th Prime Minister of Malta, 23rd Governor of New South Wales, 15th Governor of Western Australia and 9th Governor of Tasmania (d. 1940)
June 2 – Helen Herron Taft, First Lady of the United States (d. 1943)
June 12 – William Attewell, English cricketer (d. 1927)
June 13 – Richard Lawrence, failed assassin of Andrew Jackson (born c. 1800-1801)
June 19 – Doctor José Rizal, Philippine national hero (d. 1896)
June 20 – Frederick Hopkins, English biochemist, recipient of the Nobel Prize in Physiology or Medicine (d. 1947)
June 22 – Maximilian von Spee, German admiral (d. 1914)
July 10 – Alice Stevenson, British supercentenarian (d. 1973)
July 14 – Kate M. Gordon, American suffragette (d. 1932)
August 4 – Henry Head, English neurologist (d. 1940)
August 6 – Edith Roosevelt, First Lady of the United States (d. 1948)
August 7 – Spencer S. Wood, United States Navy rear admiral (d. 1940)
August 10 – Almroth Wright, British bacteriologist and immunologist (d. 1947)
September 2 – Henrietta Crosman, American stage & film actress (d. 1944)
September 10 – Niels Hansen Jacobsen, Danish sculptor and ceramist (d. 1941)
Juhani Aho, Finnish author and journalist (d. 1921)
Erich von Falkenhayn, German general (d. 1922)
Robert Bosch, German industrialist, engineer and inventor (d. 1942)
Mary Elizabeth Coleridge, British poet and novelist (d. 1907)
September 30 – William Wrigley, Jr., U.S. chewing gum industrialist (d. 1932)
October 4 – Frederic S. Remington, cowboy artist and sculptor (d. 1909)
Arvid Järnefelt, Finnish author (d. 1932)
J. B. Bury, British historian (d. 1927)
October 24 – Alexey Kaledin, Russian general (d. 1918)
October 30 – Antoine Bourdelle, French sculptor (d. 1929)
November 4 – Dimitrios Ioannou, Greek general (d. 1926)
November 6 – James Naismith, Canadian inventor of basketball (d. 1939)
November 11 – Elsa Eschelsson, Swedish scholar (d. 1911)
Lillian Russell, American singer and vaudeville star (d. 1922)
Hannes Hafstein, 1st Prime Minister of Iceland (d. 1922)
December 5 – Armando Diaz, Italian general and Marshal of Italy (d. 1928)
Aristide Maillol, French sculptor (d. 1944)
Georges Méliès, French film director (d. 1938)
December 10 – Fridtjof Nansen, Norwegian explorer, recipient of the Nobel Peace Prize (d. 1930)
Pehr Evind Svinhufvud, Prime Minister and President of Finland (d. 1944)
Charles Duryea, manufacturer of motor vehicles (d. 1938)
December 16 – Antonio de La Gándara, French painter (d. 1917)
December 20 – Ivana Kobilca, Slovenian painter (d. 1926)
December 29 – Kurt Hensel, German mathematician (d. 1941)
Dixie Haygood, American magician (d. 1915)
William H. Stayton, American founder of the Association Against the Prohibition Amendment (d. ? )
Vengayil Kunhiraman Nayanar, Malayali journalist and short story writer (d. 1914)
Kallirhoe Parren, founder of the Greek women's movement (d. 1940)
Victoire Jean-Baptiste, Haitian politician (d. 1923)
January 2 – King Frederick William IV of Prussia (b. 1795)
January 17 – Lola Montez, Irish-born dancer and mistress of King Ludwig I of Bavaria (b. 1821)
January 19 – Albert Niemann, German chemist (b. 1834)
March 10 – Taras Shevchenko, Ukrainian poet (b. 1814)
March 16 – Princess Victoria, Duchess of Kent and Strathearn, mother of Queen Victoria (b. 1786)
April 15 – Isaiah Stillman, U.S. Army Major in the Black Hawk War (b. 1793)
May 29 – Joachim Lelewel, Polish nationalist historian (b. 1786)
June 3 – Stephen A. Douglas, U.S. Senator from Illinois and Presidential candidate (b. 1813)
June 25 – Abdülmecid I, Ottoman Sultan (b. 1823)
June 29 – Elizabeth Barrett Browning, English poet (b. 1806)
July 22 – Barnard Elliott Bee, Jr., Confederate general (b. 1824)
July 25 – Jonas Furrer, member of the Swiss Federal Council (b. 1805)
August 12 – Eliphalet Remington, gunsmith and founder of Remington Arms (b. 1793)
August 17 – Alcée Louis la Branche, American politician (b. 1806)
August 22 – Xianfeng Emperor, Qing dynasty the 9th emperor (b. 1831)
August 24 – Pierre Berthier, French geologist (b. 1782)
August 28 – William Lyon Mackenzie, Scottish journalist, 1st Mayor of Toronto (b. 1795)
September 7 – Willie Person Mangum, American politician (b. 1792)
October 5 – Antoni Melchior Fijałkowski, Polish bishop (b. 1778)
October 26 – Edward "Ned" Kendall, American bandleader and instrumentalist (keyed bugle) (b. 1808)
October 31 – Guillermo (William) Miller, English-born military leader in Peru (b. 1795)
November 11 – King Pedro V of Portugal (b. 1837)
December 14 – Prince Albert, husband of Queen Victoria (b. 1819)
December 18 – Ernst Anschütz, German teacher, organist, poet, and composer (b. 1780)
1861 (MDCCCLXI) was a common year starting on Tuesday (dominical letter F) of the Gregorian calendar and a common year starting on Sunday (dominical letter A) of the Julian calendar, the 1861st year of the Common Era (CE) and Anno Domini (AD) designations, the 861st year of the 2nd millennium, the 61st year of the 19th century, and the 2nd year of the 1860s decade. As of the start of 1861, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.