| January 1 | Yucatan declares independence from Mexico |
| January 21 | 1st edition of Charles Dickens' "Daily News" |
| January 28 | Battle of Allwal, Brits beat Sikhs in Punjab (India) |
| February 1 | Theophile Gautier publishes "Hashish Club" about his initiation |
| February 4 | Mormons leave Nauvoo, Mo for settlement in west |
| February 5 | "Oregon Spectator" is 1st newspaper to be published on the West Coast |
| February 10 | Beginning of Mormon march to west US |
| February 10 | British defeat Sikhs in battle of Sobraon, India |
| February 16 | Battle of Sobraon ends 1st Sikh War in India |
| February 19 | Texas state government formally installed in Austin |
| February 20 | British occupy Sikh citadel of Lahore |
| February 21 | 1st U.S. woman telegrapher, Sarah G. Bagley, Lowell, Mass |
| February 23 | Polish revolutionaries march on Cracow, but are defeated |
| March 13 | Friedrich Hebbel's "Maria Magdalena," premieres in Konigsberg |
| May 1 | Ida Pfeiffer (48) begins trip around world |
| May 3 | Mexican army surrounds fort in Texas |
| May 4 | U.S. state Michigan ends death penalty |
| May 8 | 1st major battle of Mexican War fought at Palo Alto Texas |
| May 9 | Battle of Resaca de la Palma-U.S. sends Mexico back to Rio Grande |
| May 13 | U.S. declares war on Mexico, 2 months after fighting begins |
| May 17 | Saxophone is patents by Antoine Joseph Sax |
| May 18 | U.S. troops attack Rio Grande occupying Matamoros |
| May 21 | 1st steamship arrives in Hawaii |
| May 24 | General Zachary Taylor captures Monterey in Mexican War |
| June 5 | Telegraph line opens between Philadelphia and Balt |
| June 8 | Battle at Gwanga: British troops beat Bantu |
| June 10 | Robert Thomson obtains an English patent on a rubber tire |
| June 14 | Belgian Liberal Party forms |
| June 14 | California declares independence from Mexico in Sonoma |
| June 15 | Oregon Treaty signed, setting US-British boundary at 49 degrees N |
| June 19 | 1st baseball game (Cartwright Rules)-NY Nines 23, Knickerbockers 1 |
| June 24 | Residency tax on Jews of Hungary abolished |
| July 7 | U.S. annexs California |
| July 9 | Captain Montgomery claims Yerba Buena, San Francisco, for U.S. |
| July 21 | Mormons found 1st English settlement in California (San Joaquin Valley) |
| August 5 | Oregon country divided between U.S. and Britain at 49th parallel |
| August 10 | Congress charters "nation's attic," Smithsonian Institution |
| August 14 | Henry David Thoreau jailed for tax resistance |
| August 16 | Gioacchino Rossini marries Olympe Pelissier in Paris |
| August 17 | U.S. fleet officer Robert F Stockton annexes California |
| August 18 | General Stephen W Kearney's U.S. forces captures Santa Fe, New Mexico |
| August 22 | U.S. annexes New Mexico |
| August 26 | Felix Mendelssohn's "Elijah," premieres |
| August 26 | W A Bartlett appointed 1st U.S. mayor of Yerba Buena (SF) |
| September 10 | Elias Howe patents sewing machine |
| September 10 | Japan invents the rickshaw |
| September 15 | Jung Bahadur Rana grabs power in Nepal |
| September 18 | Elizabeth Barrett and R Browning exchange last letters before eloping |
| September 19 | Elizabeth Barrett and Robert Browning elopes |
| September 23 | Johann Gottfried Galle and Heinrich d'Arrest find Neptune |
| September 25 | U.S. troops under General Taylor occupies Monterey Mexico |
| September 30 | Anesthetic ether used for 1st time (Dr. Wm Morton extracts a tooth) |
| October 10 | Alexis the Tocqueville writes about "Algerian problem" |
| October 10 | Neptune's moon Triton discovered by William Lassell |
| October 15 | Dr. William Thomas Green Morton 1st public use of ether |
| October 16 | Dentist William T Morton demonstrates effectiveness of ether |
| October 28 | Pioneers suffer blizzard in Sierra Nevada; 42 die |
| October 31 | Donner party, unable to cross the Donner Pass, construct a winter camp |
| November 4 | Benjamin Palmer patents artificial leg |
| November 5 | Robert Schumann's 2nd Symphony in C, premieres |
| December 5 | C F Schoenbein obtains patent for cellulose nitrate explosive |
| December 6 | Opera "La Damnation de Faust" is produced (Paris) |
| December 8 | Hector Berlioz's "La Damnation de Faust," premieres |
| December 28 | Iowa becomes 29th state |
