Charles Fort: A Fortean Chronology, 1921.

"J.C.H. macbeth, London Manager of the Marconi Wireless Telegraph Company, Ltd., told several hundred men, at a luncheon of the Rotary Club, of New York, yesterday, that Signor Marconi believed he had intercepted mesages from Mars, during recent atmospheric experiments with wireless aboard his yacht Electra, in the Mediterranean."

New York Tribune, September 2, 1921.

January

• January 1: Several irregular, black objects, crossed the fiery sphere of the sun. To the Rev. William ellison they resembled pieces of burnt paper. (Books525)
• January 2: The first religious radio broadcast is heard over station (KDKA AM in Pittsburgh, Pennsylvania).
• January 2: The Spanish liner Santa Isabel sinks off Villa Garcia; 244 die.
• January 20: The Royal Navy K-boat K5 sinks in the English Channel with all 56 hands on board.

February

• February 6: The Democratic Republic of Georgia is occupied by Bolshevist Russia during the Red Army invasion of Georgia.
• February 25: the Red Army entered Georgian capital Tbilisi and installed a Moscow directed communist government.
• February 27: The International Working Union of Socialist Parties is formed in Vienna.

March

• March 4: Warren G. Harding is inaugurated as the 29th President of the United States.
• March 8: Spanish Premier Eduardo Dato Iradier is assassinated while exiting the parliament building in Madrid.
• March 14: Armenian Soghomon Tehlirian assassinates Mehmed Talaat, former Interior Minister of Turkey, in Charlottenburg, Berlin.
• March 17: Marie Stopes opens the first birth control clinic in London, England.
• March 18: The second Peace of Riga ends the Polish-Soviet War. A permanent border is established between the Polish and Soviet states.

April

• The Allies of World War I reparations commission announce that Germany has to pay 132 billion gold marks ($33 billion) in annual installments of 2.5 billion gold marks.
• April 14: In Britain, labour unions for mining, railway and transportation workers call for a strike; the government threatens to call in the army.
• April 20: Ferenc Molnár's play Liliom is first produced on Broadway in English. A flop in its native Hungary when first presented there in 1909, the American production is critically acclaimed and becomes a modern classic, filmed more than once, and eclipsed only when Rodgers and Hammerstein adapt it in 1945 into a hit musical, Carousel, which becomes a stage classic in its own right.

May

• May: A kitten is born in Nice, France. it has a white belly upon which, in grey fur, are the numerals 1921. (Books964)
• May 1-7: The riots at Jaffa (Mandatory Palestine) result in 47 Jewish and 48 Arab deaths.
• May 6: A general strike begins in Norway.
• May 14-15: Major geomagnetic storm.
• May 19: The Emergency Quota Act passes the U.S. Congress, establishing national quotas on immigration.
• May 24: Elections are held for the first time for the new Northern Ireland Parliament.
• May 31: Tulsa Race Riot - The official death toll is 39, but recent investigations suggest the actual toll may be much higher.

June

July

• July 1: The Communist Party of China is officially founded.
• July 1: A coal strike ends in England.
• July 11: The Irish War of Independence comes to an end when a truce is signed between the British Government and Irish forces.
• July 14: A Massachusetts jury finds Nicola Sacco and Bartolomeo Vanzetti guilty of first degree murder following a widely-publicized trial.
• July 18: The first BCG vaccination against tuberculosis is given.
• July 25: A loud report, followed by a tremor and a rumbling sound at Comrie, Scotland. (Books525)
• July 27: Researchers at the University of Toronto led by biochemist Frederick Banting announce the discovery of the hormone insulin.
• July 29: Adolf Hitler becomes Führer of the Nazi Party.
• July 31: a fall of little frogs upon the farm of Anton Wagner, Stirling, Conn. (Books525)

August

• The United States formally ends World War I, declaring a peace with Germany.
• August 6: Dr. Emmert of Detroit observes an unknown luminous object near the sun. (Books526)
• August 7: An unknown luminous object is seen, near the sun, at Mt. Hamilton, by an astronomer, Prof Campbell. (Books525). A severe shock (earthquake) at Canton, Virginia. (Books526)
• August 11: The temperature reaches 39 degrees Celsius in Breslau; the heat wave continues elsewhere in Europe as well.
• August 17: Innumerable little frogs appeared during a thunderstorm, in the streets of northern London. (Books545)
• August 24: Airship ZR 2 explodes during a test flight near Hull, England; 41 are killed.
• August 26: Rising prices cause major riots in Munich. The assassination of German politician Matthias Erzberger causes the government to declare martial law.
• August 26: "Invisible hands"  sieze the hands of a motorcycle rider on a Dartmoor road, forcing the machine onto the turf and the rider to be thrown from his motorcycle. (Books958)

September

• September 1: Poplar Strike in London: Nine members of the Poplar borough council are arrested.
• September 8: Sixteen-year-old Margaret Gorman wins the Atlantic City Pageant's Golden Mermaid trophy; pageant officials later dub her the first Miss America.
• September 21: The Oppau explosion occurs at BASF's nitrate factory in Oppau, Germany; 500-600 are killed.

October

• October 19: A massacre in Lisbon claims the lives of Portuguese Prime Minister António Granjo and other politicians.
• October 21: A peace conference between Ireland and the United Kingdom begins in London.
• October 29: Construction of the Link River Dam, a part of the Klamath Reclamation Project, is completed.

November

• November: For several weeks there were "mysterious stonethrowing by invisible agencies" at the houses of Mr Gibbons Joseph and Mr H.J. Minnaar, South Africa. (Books565)
• November 9: Riots in Reykjavík injure most of the small police force.
• November 9: Albert Einstein is awarded the Nobel Prize in Physics for his work with the photoelectric effect.
• November 11: During an Armistice Day ceremony at Arlington National Cemetery, the Tomb of the Unknowns is dedicated by U.S. President Warren G. Harding.

December

• December 1: Rising prices cause riots in Vienna.
• December 6: The Anglo-Irish Treaty establishing the Irish Free State, an independent nation incorporating 26 of Ireland's 32 counties, is signed in London.
• December 6: Agnes Macphail becomes the first woman to be elected to the Canadian Parliament.
• December 13: In the Four Power Treaty on Insular Possessions, Japan, the United States, United Kingdom, and France agree to recognize the status quo in the Pacific.