The following is a partial list of events from the year 1812 in the United States. After years of increasing tensions, the United States declares war on the British Empire, starting the War of 1812.
Lieutenant Governor of Kentucky: Gabriel Slaughter (political party unknown) (until month and day unknown), Richard Hickman (political party unknown) (starting month and day unknown)
Lieutenant Governor of Massachusetts: William Gray (political party unknown) (until month and day unknown), William Phillips, Jr. (political party unknown) (starting month and day unknown)
Lieutenant Governor of New York: DeWitt Clinton (Democratic-Republican)
January – The New England Journal of Medicine is first published in Boston by Dr John Collins Warren as the New England Journal of Medicine and Surgery and the Collateral Branches of Medical Science.
January 10 – New Orleans, the first steamship on the Mississippi River, arrives in its namesake city, completing its maiden voyage.
February 2 – Russia establishes a fur trading colony at Fort Ross, California.
February 7 – The last of four major New Madrid earthquakes strike New Madrid, Missouri, with an estimated moment magnitude of over 8.
March 26 – The Boston Gazette prints a political cartoon coining the term "Gerrymander" after former MassachusettsGovernorElbridge Gerry's approval (on February 11) of legislation creating oddly shaped electoral districts designed to help incumbents win re-election.
April–June[]
The original "Gerrymander"
April 4 – U.S. PresidentJames Madison enacts a 90-day embargo on trade with the United Kingdom.
April 20 – George Clinton, Vice President of the United States, dies in office.
April 30 – Louisiana is admitted as the 18th U.S. state (seeHistory of Louisiana).
May 8 - Hail to the Chief is published as the presidential anthem of the United States.
June 1 – War of 1812: U.S. PresidentJames Madison asks the U.S. Congress to declare war on Great Britain.
June 4 – Following Louisiana's admittance as a U.S. state, the territory created by that name is renamed the Missouri Territory.
June 18 – The War of 1812 begins between the United States and the British Empire.
July–September[]
August 19: USS Constitution sinks HMS Guerriere
July 12 – Americans invade Canada at Windsor, Upper Canada.
August 5 – War of 1812: Tecumseh's Indian force ambushes Thomas Van Horne's 200 Americans at , causing them to flee and retreat.
August 7 – 130 Filibusters of the Gutiérrez–Magee Expedition cross from Louisiana into Spanish Texas, soon after they capture the town of Nacogdoches.
August 15 – War of 1812: Battle of Fort Dearborn – Potawatomi warriors overrun the U.S. fort in Illinois Territory.
August 16 – War of 1812: American GeneralWilliam Hull surrenders Fort Detroit without a fight to the British Army.
August 19 – War of 1812, USS Constitution vs HMS Guerriere: USS Constitution defeats the British frigate HMS Guerriere off the coast of Nova Scotia. The British shot is said to have bounced off Constitution's sides, earning her the nickname "Old Ironsides".
September 13; Gutiérrez–Magee Expedition: The Expedition, having since grown to 300 men, captures the town of Santísima Trinidad de Salcedo.
October–December[]
October – The capital of Pennsylvania is permanently moved from Lancaster to Harrisburg.
October 9 – War of 1812: American naval forces under Lieutenant Jesse Duncan Elliott capture two British warships, HMS Detroit and HMS Caledonia.
October 13 – War of 1812 – Battle of Queenston Heights: As part of the Niagara campaign in Upper Canada, United States forces under General Stephen Van Rensselaer are repulsed from invading Canada by British and native troops led by Sir Isaac Brock (although he dies during the battle).
November 5 – James Madison defeats DeWitt Clinton in the U.S. presidential election.
November 13 – Gutiérrez-Magee Expedition: Manuel María de Salcedo, the governor of Spanish Texas, begins a four month long siege of Presidio La Bahia near Goliad. The siege continues until February 19, 1813.
The Williamsport Academy for the Education of Youth is founded in Pennsylvania.
The Old Oscar Pepper Distillery (now the Woodford Reserve Distillery), the oldest KentuckyBourbondistillery, is established along in Woodford County, Kentucky.
now Wayland Baptist Theological Seminary is founded by Escaped and Free Slaves in Philadelphia, Pennsylvania.
Princeton Theological Seminary is founded in New Jersey.
April 16 – Sarah Harris Fayerweather, African-American whose 1832 admission to a Connecticut school resulted in the first integrated schoolhouse (died 1878)
May 4 – John W. Stevenson, United States Senator from Kentucky from 1871 to 1877 (died 1886)
May 6 – Martin Delany, African-American abolitionist, journalist, and physician (died 1885)
May 17 – Elias Nelson Conway, 5th Governor of Arkansas from 1852 to 1860 (died 1892)
May 30 – John Alexander McClernand, lawyer, politician, and Union General during the American Civil War (died 1900)
July 27 – Thomas Lanier Clingman, North Carolina congressman, senator, and confederate general (died 1897)
July 30 – Harrison Ludington, 13th Governor of Wisconsin from 1876 to 1878 (died 1891)
August 11 – Joseph Projectus Machebeuf, French-American Catholic missionary and the first Bishop of Denver (died 1889)
August 18 – John Hugh Means, 64th Governor of South Carolina from 1850 to 1852 (died 1862)
August 22 – Joseph Mozier, American-born sculptor best known for his work in Italy. (died 1870)
September 13 – John McMurtry, builder and architect (died 1890)
September 18 – Herschel Vespasian Johnson, United States Senator from Georgia from 1863 to 1865 (died 1880)