1865 in the United States
- President: Abraham Lincoln (R-Illinois) (until April 15), Andrew Johnson (D-Tennessee) (starting April 15)
- Vice President:
- Chief Justice: Salmon P. Chase (Ohio)
- Speaker of the House of Representatives: Schuyler Colfax (R-Indiana)
- Congress: 38th (until March 4), 39th (starting March 4)
- January 13 – American Civil War: The Second Battle of Fort Fisher begins when United States forces launch a major amphibious assault against the Confederate stronghold of Fort Fisher, North Carolina.
- January 15 – American Civil War: United States forces capture Fort Fisher.
- January 31 – American Civil War: Confederate General Robert E. Lee becomes general-in-chief.
- February 17 – American Civil War: Columbia, South Carolina burns as Confederate forces flee from advancing Union forces.
- February 22 – Tennessee adopts a new constitution that abolishes slavery.
- March 3 – The U.S. Congress authorizes formation of the Freedmen's Bureau.
- March 4 – U.S. President Abraham Lincoln is inaugurated for a second term; Andrew Johnson becomes Vice President.
- March 13 – American Civil War: The Confederate States of America agrees to the use of African American troops.
- March 18 – American Civil War: The Congress of the Confederate States of America adjourns for the last time.
- March 19 – American Civil War: The Battle of Bentonville begins; by the end of the battle on March 21 the Confederate forces retreat from Four Oaks, North Carolina.
- March 21 – The University of Kansas was founded when the Board of Regents held its first meeting.
- March 25
- American Civil War: In Virginia, Confederate forces capture Fort Steadman from the Union. Lee's army suffers heavy casualties during the Battle of Fort Stedman—about 2,900, including 1,000 captured in the Union counterattack. Confederate positions are weakened. After the battle, Lee's defeat is only a matter of time.
- The "Claywater Meteorite" explodes just before reaching ground level in Vernon County, Wisconsin; fragments having a combined mass of 1.5 kg are recovered.
- April 1 – American Civil War – Battle of Five Forks: In Petersburg, Virginia, Confederate General Robert E. Lee begins his final offensive.
- April 2 – American Civil War: "Evacuation Sunday": Confederate President Jefferson Davis and most of his Cabinet flee the Confederate capital of Richmond, Virginia, which is taken by Union troops the next day.
- April 3 –American Civil War: Richmond is captured by Union forces under General Ulysses S. Grant.
- April 9 – American Civil War: General Robert E. Lee surrenders to Ulysses S. Grant at Appomattox Court House, effectively ending the American Civil War.
- April 14 (Good Friday)
- Assassination of Abraham Lincoln: Actor and Confederate sympathizer John Wilkes Booth shoots and mortally wounds U. S. President Abraham Lincoln while Lincoln is attending an evening performance of the farce Our American Cousin at Ford's Theatre in Washington, D.C.. Doctors attend the President in the theater then soldiers move his unconscious body to a boarding house across the street. Because of his height, Lincoln is laid diagonally across a bed so his body will fit.
- U.S. Secretary of State William H. Seward and his family are attacked in his home by Lewis Powell.
- April 15 – Inauguration of Andrew Johnson: President Lincoln dies of his gunshot wound early this morning and Vice President Andrew Johnson becomes the 17th President of the United States.
- April 18 – Confederate President Jefferson Davis and his entire cabinet arrive in Charlotte with a contingent of 1,000 soldiers.
- April 26
- April 27
- May 4 – American Civil War: Lieutenant General Richard Taylor, commanding all Confederate forces in Alabama, Mississippi, and eastern Louisiana, surrenders his forces to Union General Edward Canby at Citronelle, Alabama, effectively ending all Confederate resistance east of the Mississippi.
- May 5
- May 10 – American Civil War: Jefferson Davis is captured by Union troops near Irwinville, Georgia.
- May 12–May 13 – American Civil War – Battle of Palmito Ranch: In far south Texas, more than a month after Confederate General Lee's surrender, the last land battle of the civil war with casualties ends with a Confederate victory.
- May 23 – Grand Review of the Armies: Union Army troops parade down Pennsylvania Avenue (Washington, D.C.) to celebrate the end of the American Civil War.
- May 25 – Mobile magazine explosion: 300 are killed in Mobile, Alabama when an ordnance depot explodes.
- May 26 – Indigenous tribes who supported the Confederate States of America hold the Camp Napoleon Council in Indian Territory.
- June 2 – American Civil War: Confederate forces west of the Mississippi under General Edmund Kirby Smith surrender at Galveston, Texas under terms negotiated on May 26, becoming the last to do so.
- June 19 – American Civil War: Union Major General Gordon Granger lands at Galveston, Texas and informs the people of Texas of the Emancipation Proclamation. (an event celebrated in modern times each year as Juneteenth).
- June 23 – American Civil War: At Fort Towson in Indian Territory, Confederate General Stand Watie, a Cherokee Indian, surrenders the last significant Confederate army.
- July 5 – The U.S. Secret Service is founded.
- July 6 – The Nation political magazine begins publication.
- July 7 – Following Abraham Lincoln's assassination on April 14, the 4 conspirators condemned to death during the trial are hanged, including David Herold, George Atzerodt, Lewis Payne and Mary Surratt. Her son, John Surratt, escapes execution by fleeing to Canada, and ultimately to Egypt.
- July 21 – Wild Bill Hickok – Davis Tutt shootout: In the market square of Springfield, Missouri, Wild Bill Hickok shoots Little Dave Tutt dead over a poker debt in what is regarded as the first true western "fast draw" showdown.
- July 30 – The steamer Brother Jonathan sinks off the California coast, killing 225.
- September 8– 21: Fort Smith Council between U. S. and Native American tribes that had supported the Confederated States of America regarding Reconstruction Treaties.
- October 8 – The 6.3 Mla Santa Cruz Mountains earthquake shook the Central Coast and San Francisco Bay Area of California with a maximum Mercalli intensity of VIII (Severe), causing $500,000 in damage.
- October 25 – The paddlewheel steamer SS Republic sinks off the Georgia coast, with a cargo of $400,000 in coins.
- November 6 – American Civil War: Surrender to the British at Liverpool of the commerce raider CSS Shenandoah (Captain James Waddell), the last significant organized Confederate unit.
- November 10 – Major Henry Wirz, the superintendent of a prison camp in Andersonville, Georgia, is hanged, becoming the only American Civil War soldier to be executed for war crimes.
- November 18 – Mark Twain's story "The Celebrated Jumping Frog of Calaveras County" is published in the New York weekly The Saturday Press in its original version as "Jim Smiley and His Jumping Frog".
- December 11 – The U.S. Congress creates the House Appropriations Committee and the Committee on Banking and Commerce, reducing the tasks of the Committee on Ways and Means.
- December 18 – The Thirteenth Amendment to the United States Constitution (which forever abolishes slavery) is declared ratified by three-quarters of the states of the United States.
- December 21 – The Kappa Alpha Order is founded at Washington and Lee University.
- December 24 – The Ku Klux Klan is formed by six Confederate Army veterans, with support of the Democratic Party, in Pulaski, Tennessee, to resist Reconstruction and intimidate "carpetbaggers" and "scalawags", as well as to repress the freed slaves.
- January 5 – Johnson N. Camden, Jr., U.S. Senator from Kentucky from 1914 to 1915 (died 1942)
- January 10 – Mary Ingalls, blind older sister of author Laura Ingalls Wilder (died 1928)
- January 28 – Verina Morton Jones, African American physician, suffragist and clubwoman (died 1943)
- February 1 – Henry Luke Bolley, plant pathologist (died 1956)
- February 28 – Alexander Henderson, businessman (died 1925)
- March 19 – William Morton Wheeler, entomologist (died 1937)
- April 28 – Charles W. Woodworth, entomologist (died 1940)
- May 2 – Clyde Fitch, dramatist (died 1909)
- May 3 – Henry Francis Bryan, governor of American Samoa (died 1944)
- May 25 – John Mott, YMCA leader, recipient of the Nobel Peace Prize (died 1955)
- May 26 – Robert W. Chambers, artist (died 1933)
- June 25 – Robert Henri, painter, leader of the Ash Can School (died 1929)
- June 29 – William Borah, U.S. Senator from Idaho from 1907 to 1940 (died 1940)
- July 14 – Arthur Capper, U.S. Senator from Kansas from 1919 to 1949 (died 1951)
- August 2 – Irving Babbitt, literary critic (died 1933)
- August 27
- September 24 – Mollie McConnell, actress (died 1920)
- October 14 – Mary Margaret O'Reilly, Assistant Director of the United States Mint (died 1949)
- October 15 – Charles W. Clark, baritone (died 1925)
- October 17 – James Rudolph Garfield, politician (died 1950)
- October 22 – Raymond Hitchcock, actor (died 1929)
- October 26 – Benjamin Guggenheim, businessman (died 1912)
- November 2 – Warren G. Harding, 29th President of the United States from 1921 until 1923 (died 1923)
- December 19 – Minnie Maddern Fiske, stage actress (died 1932)
- December 20 – Elsie de Wolfe, socialite and interior decorator (died 1950)
- December 25 – Fay Templeton, singer and actress (died 1939)
- March 10 – Amy Spain, slave, hanged (born c.1848)
- April 2 – A. P. Hill, Confederate general killed in the American Civil War (born 1825)
- April 15 – Abraham Lincoln, 16th President of the United States from 1861 to 1865 (born 1809)
- April 26 – John Wilkes Booth, actor and assassin of Abraham Lincoln (born 1838)
- May 20 – William K. Sebastian, U.S. Senator from Arkansas from 1848 to 1861 (born 1812)
- May 21 – Jeremiah Clemens, U.S. Senator from Alabama from 1849 to 1853 (born 1814)
- July 6 – William Quantrill, Confederate leader during the American Civil War (born 1837)
- June 10 – Mrs Lydia Sigourney, the "Sweet Singer of Hartford", poet (born 1791)
- June 23 – Samuel Francis Du Pont, rear admiral (born 1803)
- July 7
- George Atzerodt, conspirator with John Wilkes Booth, assigned to assassinate Vice President Andrew Johnson (born 1835)
- David Herold, conspirator with John Wilkes Booth (born 1842)
- Lewis Powell, conspirator with John Wilkes Booth, attempted assassin of William H. Seward (born 1844)
- Mary Surratt, conspirator with John Wilkes Booth, first woman executed by American federal government (born either 1820 or 1823)
- August 25 – John Drew, Cherokee Confederate colonel of the First Mounted Cherokee Regiment (born 1796 in the Cherokee Nation East)
- November 29 – Isaac A. Van Amburgh, animal trainer (born 1811)
- December 16 – Philip Allen, U.S. Senator from Rhode Island from 1853 to 1859 (born 1785)
- American Annual Cyclopaedia ... 1865, NY: D. Appleton & Co. – via HathiTrust
- Media related to 1865 in the United States at Wikimedia Commons
- Booknotes interview with Jay Winik on April 1865: The Month That Saved America, July 29, 2001.
- "1865". Timeline. Digital Public Library of America.