| January 5 | California Exchange opens |
| January 18 | British blockade Piraeus, Greece to enforce mercantile claims |
| January 20 | Investigator, 1st ship to effect northwest passage, leaves England |
| January 22 | Alta California becomes a daily paper, 1st such in Calif |
| January 26 | 1st German-language daily newspaper in U.S. published, New York City |
| January 29 | Henry Clay introduces a comprise bill on slavery to U.S. Senate |
| February 5 | Adding machine employing depressible keys patented, New Paltz, New York |
| February 12 | Original Washington's Farewell Address manuscript sells for $2,300 |
| February 18 | California Legislature creates 9 Bay Area counties |
| March 7 | Daniel Webster endorses Compromise of 1850 |
| March 11 | Woman's Medical College of Penn (1st female medical school) |
| March 12 | 1st U.S. $20 gold piece issued |
| March 16 | Nathaniel Hawthorne's "Scarlet Letter" published |
| March 18 | Henry Wells and William Fargo forms American Express in Buffalo |
| March 29 | Ireland's SS Royal Adelaide sinks in storm; 200 die |
| March 31 | U.S. population hits 23,191,876 (Black population: 3,638,808 (15.7%)) |
| April 1 | San Francisco County Government established |
| April 4 | City of Los Angeles incorporated |
| April 15 | City of San Francisco incorporated |
| April 25 | Paul Julius Reuter, use 40 pigeons to carry stock market prices |
| May 1 | John Geary becomes 1st San Francisco mayor |
| May 11 | Work starts on 1st brick building in San Francisco |
| May 27 | Mormon Temple in Nauvoo, Illinois destroyed by tornado |
| June 4 | Empire Engine Company No 1 organized |
| June 4 | Self deodorizing fertilizer patented in England |
| June 6 | Levi Strauss made his 1st blue jeans |
| June 10 | Millard Fillmore sworn-in as president of U.S. (replacing Taylor) |
| June 14 | Fire destroys part of San Francisco |
| June 17 | Paddle-wheeler "G P Griffith" burns off Mentor Ohio, 206 die |
| June 19 | Swedish/Norwegian crown prince Charles weds Dutch princess Wilhelmina |
| June 29 | British ex-premier sir Robert Peel falls off his horse |
| July 1 | At least 626 ships lie at anchor around San Francisco Bay |
| July 2 | Benjamin Lane patents gas mask with a breathing apparatus |
| July 7 | Scottish explorer Edward Eyre reaches Albany, W-Australia |
| July 10 | Vice President Fillmore becomes President following Zachary Taylor's death |
| July 12 | Dutch 2nd Chamber accepts establishment of Provincial States |
| July 14 | 1st public demonstration of ice made by refrigeration |
| July 15 | John Wisden bowls all 10 South batsmen, North vs. South at Lord's |
| July 17 | Harvard Observatory takes 1st photograph of a star, Vega |
| July 19 | Airship Elizabeth leaves in storm for Fire Island, crashes (42 die) |
| July 23 | 17th Postmaster General: Nathan K Hall of New York takes office |
| July 25 | Gold discovered in Oregon, Rogue River |
| August 23 | 1st national women's rights convention convenes in Worcester Mass |
| August 28 | Richard Wagner's opera "Lohengrin" premieres at Weimar Germany |
| August 30 | Honolulu, Hawaii becomes a city |
| September 9 | California becomes 31st state |
| September 9 | Territories of New Mexico and Utah created |
| September 11 | "Swedish Nightingale" Jenny Lind gives 1st U.S. concert |
| September 17 | Great fire in San Francisco |
| September 18 | Congress passes Fugitive Slave Law as part of Compromise of 1850 |
| September 20 | Slave trade abolished in DC, but slavery allowed to continue |
| September 24 | Papal Bull issued, establishes Roman Catholic hierarchy in England |
| September 28 | U.S. Navy abolishes flogging as punishment |
| October 12 | 1st women's medical school (Women's Medical College of Penns), opens |
| October 17 | Knickerbocker Engine Co Number 5 organized |
| November 6 | 1st Hawaiian fire engine |
| November 6 | Yerba Buena and Angel Islands (SF Bay) reserved for military use |
| November 19 | Lord Tennyson becomes British poet laureate |
| December 20 | Hawaiian post office established |
| December 27 | Hawaiian Fire Department established |
| December 28 | Rangoon Burma, destroyed by fire |
