Year 1870 (MDCCCLXX) was a common year starting on Saturday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Thursday of the 12-day slower Julian calendar).

Events of 1870

January - March

• January 1
  • First edition of The Northern Echo newspaper published.
  • Plans for the Brooklyn Bridge are completed.
• January 3 - Construction of the Brooklyn Bridge begins.
• January 6 - The inauguration of the Musikverein (Vienna).
• January 10 - John D. Rockefeller incorporates Standard Oil.
• January 15 - A political cartoon for the first time symbolizes the United States Democratic Party with a donkey ("A Live Jackass Kicking a Dead Lion" by Thomas Nast for Harper's Weekly).
• January 26 - Reconstruction: Virginia rejoins the Union.
• January 27 - First college sorority, Kappa Alpha Theta, is established at DePauw University.
• February - Vrain Denis-Lucas in sentenced for two years in prison for multiple forgery in Paris.
• February 1 - Goodna State School in Goodna, Queensland, Australia is founded.
• February 2 - It is revealed that the famed Cardiff Giant was just carved gypsum and not the petrified remains of a human.
• February 3 - The 15th Amendment to the United States Constitution is passed.
• February 10
  • Anaheim, California is incorporated.
  • The YWCA is founded in New York City.
• February 12 - Women gain the right to vote in Utah Territory.
• February 23 - Military control of Mississippi ends and it's readmitted to the Union.
• February 25 - Hiram Rhodes Revels, a Republican from Mississippi, is sworn into the United States Senate, becoming the first African American ever to sit in the U.S. Congress.
• February 26 - In New York City, the first pneumatic-subway is opened.
• February 28 - The Bulgarian Exarchate is established by decree of Sultan Abd-ul-Aziz of the Ottoman Empire.
• March 2 - Francisco Solano López' last troops cornered by Triple Alliance troops at Cerro Cora. López refuses to surrender and is killed. Fighting ends in Paraguay - the War of the Triple Alliance is over.
• March 3 - Thomas Scott is executed by Louis Reil's provisional government during the Red River Rebellion in modern day Manitoba Canada.
• March 19 - Ohio Legislature passes the Cannon Act, thereby establishing the Ohio Agriculture and Mechanical College, later The Ohio State University.
• March 24 - Syracuse University is established and officially opens.
• March 30
  • The 15th Amendment is entered into the United States Constitution, giving blacks the right to vote.
  • Texas is readmitted to the Union following Reconstruction.
• March 31 - Thomas Mundy Peterson the first African-American to vote in an election.

April - June