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1855 (MDCCCLV)was a common year starting on Monday of the Gregorian calendar and a common year starting on Saturday of the Julian calendar, the 1855th year of the Common Era (CE) and Anno Domini (AD) designations, the 855th year of the 2nd millennium, the 55th year of the 19th century, and the 6th year of the 1850s decade. As of the start of 1855, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
- January 1 – Ottawa, Ontario is incorporated as a city.
- January 5 – Ramón Castilla begins his third term as President of Peru.
- January 23
- January 26 – The Point No Point Treaty is signed in the Washington Territory.
- January 27 – The Panama Railway becomes the first railroad to connect the Atlantic and Pacific Oceans.
- January 29 – Lord Aberdeen resigns as Prime Minister of the United Kingdom, over the management of the Crimean War.
- February 5 – Lord Palmerston becomes Prime Minister of the United Kingdom.
- February 11 – Kassa Hailu is crowned Tewodros II, Emperor of Ethiopia.
- February 12 – Michigan State University (the "pioneer" land-grant college) is established.
- February 15 – The North Carolina General Assembly incorporates the Western North Carolina Railroad, to build a rail line from Salisbury to the western part of the state.
- February 22 – Pennsylvania State University is founded, as the Farmers' High School of Pennsylvania.
- March 2 – Alexander II ascends the Russian throne, upon the death of his father Nicholas I.
- March 3 – The United States Congress appropriates $30,000 to create the U.S. Camel Corps.
- March 16 – Bates College is founded by abolitionists in Lewiston, Maine.
- March 17 – Taiping Rebellion: A Taiping army of 350,000 invades Anhui.
- March 30 – Elections are held for the first Kansas Territory legislature. Missourians cross the border in large numbers, to elect a pro-slavery body.
беларуская (тарашкевіца): 1855
srpskohrvatski / српскохрватски: 1855