January 1 – Abraham Lincoln signs the Emancipation Proclamation during the third year of the American Civil War, making the abolition of slavery in the Confederate states an official war goal. It proclaims the freedom of 3.1 million of the nation's four million slaves and immediately frees 50,000 of them, with the rest freed as Union armies advance.
January 2 – Master Lucius Tar Paint Company (Teerfarbenfabrik Meister Lucius), predecessor of Hoechst, as a worldwide chemical manufacturing brand, founded in a suburb of Frankfurt am Main, Germany.
January 4 – The New Apostolic Church, a Christian and chiliastic church, is established in Hamburg, Germany.
January 7 – In the Swiss canton of Ticino, the village of Bedretto is partly destroyed and 29 killed, by an avalanche.
January 8
The Yorkshire County Cricket Club is founded at the Adelphi Hotel, in Sheffield, England.
American Civil War – Second Battle of Springfield
January 10 – The first section of the London Underground Railway (Paddington to Farringdon Street) opens officially.
January 11
American Civil War – Battle of Arkansas Post: General John McClernand and Admiral David Dixon Porter capture the Arkansas River for the Union.
In the Swiss Canton Ticino, the roof of the church of Sant'Antonio in Locarno collapses under the weight of snow, killing 47.
January 12 – Swami Vivekananda, Indian Hindu monk, philosopher, author, religious teacher, and the chief disciple of the Indian mystic Ramakrishna
January 15 – French intervention in Mexico: French forces bombard Veracruz.
January 21 – Adam Opel founds Opel AG.
January 22 – The January Uprising breaks out in Poland, Lithuania and Belarus. The aim of the national movement is to liberate the Polish–Lithuanian–Ruthenian Commonwealth from Russian occupation.
January 29 – American Indian Wars – Bear River Massacre: The United States Army, led by General Patrick Edward Connor, massacres Chief Bear Hunter and forces of the Shoshone, in the Idaho Territory.
January 31 – Jules Verne's first adventure novel, Five Weeks in a Balloon (Cinq semaines en ballon), is published in Paris.