July 26 - Texas Jack Omohundro, American frontier scout
October 28 - Georges Auguste Escoffier, French chef (d. 1935)
November 7 - Ignaz Brüll, Austrian pianist (d. 1907)
November 25 - Carrie Nation, American temperance advocate (d. 1911)
Deaths
April 16 - Domenico Dragonetti, Italian composer (b. 1763)
December 23 - Jean Baptiste Bory de Saint-Vincent, French naturalist (b. 1780)
Events
January 5 - The United States House of Representatives votes to stop sharing the Oregon Territory with the United Kingdom.
January 28 - Battle of Aliwal, India won by British troops commanded by Sir Harry Smith.
January 31 - After the Milwaukee Bridge War, Juneautown and Kilbourntown unified as the City of Milwaukee, Wisconsin.
February 10 - First Anglo-Sikh War: Battle of Sobraon
February 19 - In Austin, Texas the newly-formed Texas state government is officially installed. The Republic of Texas government officially transfers power to the State of Texas government following Texas' annexation by the United States.
March 27 - Mexican-American War: Siege of Fort Texas.
April 14 - The Donner Party of pioneers departs Springfield, Illinois, for California, on what will become a year-long journey of hardship, cannibalism, and survival.
April 25 - Thornton Affair: Open conflict begins over the disputed border of Texas, triggering the Mexican-American War.
May 1 - The few remaining Mormons left in Nauvoo, Illinois, formally dedicated the Nauvoo Temple.
May 8 - Mexican-American War: The Battle of Palo Alto – Zachary Taylor defeats a Mexican force north of the Rio Grande in the first major battle of the war.
May 13 - Mexican-American War: The United States declares war on Mexico.
May 23 - Mexican-American War: President Mariano Paredes of Mexico unofficially declares war on the United States.
May 24 - Mexican-American War: General Zachary Taylor captures Monterrey.
June 15 - The Oregon Treaty establishes the 49th parallel as the border between the United States and Canada, from the Rocky Mountains to the Strait of Juan de Fuca.
June 16 - The Papal conclave of 1846 concludes. Pope Pius IX is elected pope, beginning the longest reign in the history of the papacy (not counting St. Peter).
June 19 - The first baseball game under recognizable modern rules is played in Hoboken, New Jersey, United States.
July 7 - Mexican-American War: American troops occupy Monterey and Yerba Buena, thus beginning the United States conquest of California.
July 9 - The territory of the District of Columbia south of the Potomac River (39 mi² or about 100 km²) is returned to Virginia through an Act of Congress.
August 10 - The Smithsonian Institution is chartered by the U.S. Congress after $500,000 was given for such a purpose by scientist James Smithson.
August 14 - The Cape Girardeau meteorite, a 2.3 kg chondrite-type meteorite strikes near the town of Cape Girardeau in Cape Girardeau County, Missouri.
September 10 - Elias Howe is granted a patent for the sewing machine.
September 12 - Elizabeth Barrett elopes with Robert Browning.
September 23 - Neptune is discovered by French astronomer Urbain Jean Joseph Le Verrier and British astronomer John Couch Adams; the discovery is verified by German astronomer Johann Gottfried Galle.
September 25 - U.S. forces led by Zachary Taylor capture the Mexican city of Monterrey.
December 28 - Iowa is admitted as the 29th U.S. state.
