January 2 – First Red Scare: The second of the Palmer Raids takes place with another 4,025 suspected communists and anarchists arrested and held without trial in several cities.
January 5 – 1920 United States Census count begins. This becomes the first census to record a population exceeding 100 million, at 106,021,537. Because there are so many mixed-race persons and because so many Americans with some black ancestry appear white, the Census Bureau stops counting mixed-race peoples and the one-drop rule becomes the national legal standard.
January 9 – Thousands of onlookers watch as "The Human Fly" George Polley climbs New York City's Woolworth Building. He reaches the 30th floor when a policeman arrests him for climbing without a permit.
January 13 – The New York Times ridicules the American rocket scientist Robert H. Goddard. (Decades later, on July 17, 1969, as the Apollo 11 crew head to the Moon, the newspaper will retract this editorial.)[2]
January 30 – A professional wrestling match in which Joe Stecher defeats Earl Caddock at New York City's Madison Square Garden is filmed by Pioneer Film Corporation for later viewing by cinema audiences; this is the oldest surviving movie of a pro wrestling match.[5]
June 21 – The 4.9 MLInglewood earthquake shakes the Los Angeles Area with a maximum Mercalli intensity of VIII (Severe), causing more than $100,000 in damage.
June 28 - Sigma Tau Gamma Fraternity, Incorporated is founded in Warrensburg, Missouri.
KDKA (AM) of Pittsburgh, Pennsylvania (owned by Westinghouse) starts broadcasting as a commercial radio station. The first broadcast is the results of the presidential election.
Van Wyck Brooks publishes The Ordeal of Mark Twain, arguing that Twain's genius was twisted by the conditions and culture of late 19th-century America. This begins a reassessment of Twain, who has been seen hitherto mainly as a humorous entertainer, and his contemporaries.
^"FAQs about Robert H. Goddard". Clark University. Archived from the original on November 3, 2009. Retrieved October 27, 2009. "When was the famous New York Times editorial about Dr. Goddard?"