| January 2 | 10,000 U.S. union and socialist organizers arrested (Palmer Raids) |
| January 3 | Arthur Honegger's "Chant de Nigamon," premieres |
| January 3 | New York Yankees purchase Babe Ruth from Red Sox for $125,000 |
| January 4 | Amsterdam actors decide to strike for retirement benefits |
| January 5 | Boston Red Sox sell Babe Ruth to New York Yankees |
| January 5 | New York Yankees announce purchase of Babe Ruth |
| January 10 | League of Nations established |
| January 10 | Mont Canadiens (14) and Tor St. Patricks (7) score NHL record 21 goals |
| January 10 | Silver reaches record $1.37 an ounce |
| January 11 | French passenger ship Afrique sinks near La Rochelle; 553 die |
| January 12 | Annual drafting of baseball players from minor leagues to be done in inverse order of the final standings, agreed to |
| January 13 | New York Times editorial (falsely) reports rockets can never fly |
| January 16 | 18th Amendment, prohibition, goes into effect; repealed in 1933 |
| January 16 | 1st assembly of League of Nations in Paris |
| January 16 | Georgia declares independence |
| January 17 | Paul Deschanel elected president of France |
| January 19 | Alexandre Millerand forms French government |
| January 19 | U.S. Senate votes against membership in League of Nations |
| January 20 | Dutch 2nd Chamber passes school laws |
| January 23 | Dutch refuse to turn over ex-kaiser Wilhelm I of Germany to allies |
| January 26 | Amadeo Modigliani's mistress jumps out of a window |
| January 29 | Walt Disney starts 1st job as an artist; $40 week with Kansas City Slide Co. |
| January 30 | Quebec's Joe Malone sets NHL record of 7 goals in a game |
| January 31 | 1st Ukrainian daily newspaper in U.S. (New York City) begins publication |
| January 31 | Joe Malone, Quebec Bulldogs, sets NHL record with 7 goals in a game |
| January 31 | Phi Beta Sigma Fraternity, at Howard University, incorporates |
| February 1 | 1st commercial armored car introduced in St. Paul Minn |
| February 1 | Royal Canadian Mounted Police forms as Royal Northwest Mounted Police merge with Dominion Police |
| February 1 | Soccer team Quick Boys forms |
| February 2 | Estonia declares its Independence from Russia (Dorpat Peace) |
| February 2 | France occupies (German) Memel territory |
| February 2 | Tarto/Dorpat peace treaty: U.S.S.R. recognizes Estonian independence |
| February 4 | 1st flight from London to South Africa takes-off |
| February 6 | Saarland administrated by League of Nations |
| February 8 | Swiss men vote against women's suffrage |
| February 9 | International treaty recognizes Norwegian sovereignty over Svalbard |
| February 9 | Joint Rules Com bans foreign substances and alterations to baseballs |
| February 10 | Baseball outlaws all pitches involving tampering with ball |
| February 12 | NL votes 6-2 for 1 commissioner AL votes 6-2 to keep group commission |
| February 13 | League of Nations recognizes perpetual neutrality of Switzerland |
| February 13 | Switzerland rejoin League of Nations |
| February 14 | League of Women Voters forms in Chicago |
| February 19 | Netherlands joins League of Nations |
| February 21 | Darius Milhaud and Jean Cocteau's ballet, premieres in Paris |
| February 22 | 1st artificial rabbit used at a dog race track in Emeryville, California |
| February 24 | NSDAP begins at Hofbrauhaus Munich |
| February 24 | Peace treaty gives Estonia independence |
| February 28 | Maurice Ravel's "Le tombeau de Couperin," premieres |
| March 1 | Austria becomes a kingdom again, under Adm Horthy |
| March 2 | Karel Capek's "Loupeznik," premieres in Prague |
| March 3 | Montreal Canadiens scores NHL record 16 goals beating Quebec Bulldogs |
| March 4 | Last day of Julian civil calendar in Greece |
| March 8 | Denmark and Cuba join the League of Nations |
| March 10 | NHL's Quebec Bulldog Jim Malone scores 6 goals vs Ottawa Senators |
| March 13 | Wolfgang Kapp's coup attempt in Berlin fails |
| March 16 | 1 Acre Park also known as Baby Park in the Bronx renamed Melrose Park |
| March 18 | Greece adopts the Gregorian calendar |
| March 19 | U.S. Senate rejects Treaty of Versailles for 2nd time refusing to ratify League of Nations' covenant (maintaining isolation policy) |
| March 20 | 1st flight from London to South Africa lands (1 month) |
| March 20 | U.S. Ladies Figure Skating championship won by Theresa Weld |
| March 20 | U.S. Mens Figure Skating championship won by Sherwin Badger |
| March 23 | Perserikatan Communist of India (PKI) political party forms |
| March 24 | 1st U.S. coast guard air station established (Morehead City NC) |
| March 25 | Greek Independence Day |
| March 27 | Film stars Mary Pickford and Douglas Fairbanks wed |
| March 27 | Hermann Muller becomes German chancellor (SPD) |
| March 28 | Actor Douglas Fairbanks marries actress Mary Pickford |
| March 28 | Thomas Masaryk elected president of Czechoslovakia |
| March 31 | British parliament accept Irish "Home Rule"-law |
| April 1 | Church disforms in Wales |
| April 1 | Stanley Cup: Ottawa Senators (NHL) beat Seattle (PCHA), 3 games to 2 |
| April 4 | Arabs attack Jews in Jerusalem |
| April 6 | French troop attacks Main/Darmstadt/Hanau |
| April 8 | LONGA soccer team forms in Tilburg |
| April 13 | 1st woman U.S. Civil Service Commissioner, Helen Hamilton appointed |
| April 14 | Tornadoes killed 219 people in Alabama and Mississippi |
| April 15 | New Canadian small cent coin is released |
| April 17 | American Professional Football Association forms (NFL) |
| April 19 | 24th Boston Marathon won by Peter Trivoulidas of Greece in 2:29:31 |
| April 20 | 7th modern Olympic games opens in Antwerp Belgium |
| April 20 | Balfour Declaration recognized, makes Palestine a British Mandate |
| April 20 | Big Show ends 2 year run on NBC radio |
| April 20 | Phillies manager Gravvy Cravath puts himself in as pinch hitter, his 3- run homer beats New York Giants 3-0 |
| April 20 | Tornadoes kill 219 in Alabama and Mississippi |
| April 21 | John Galsworthy's "Skin Game," premieres in London |
| April 23 | Turkish Grand National Assembly 1st meets, in Ankara |
| April 24 | British Mandate over Palestine goes into effect, lasts 28 years |
| April 24 | Polish troops attack Ukraine |
| April 26 | H Shapley and H D Curtis hold "great debate" on nature of nebulae |
| April 27 | Pogrom leader Petljoera declares Ukraine Independence |
| April 28 | Azerbaijan SSR joins U.S.S.R. (1st time) |
| May 1 | Babe Ruth's 1st Yankee HR and 50th of career, out of Polo Grounds |
| May 1 | Belgian-Luxembourg toll tunnel opens |
| May 1 | Brooklyn Dodgers tie Boston Braves, 1-1, in 26 innings |
| May 5 | German-Latvian peace treaty signed |
| May 5 | Polish troops occupy Kiev |
| May 5 | U.S. President Wilson makes Communist Labor Party illegal |
| May 7 | U.S.S.R. recognizes Georgia's independence |
| May 8 | 46th Kentucky Derby: Ted Rice aboard Paul Jones wins in 2:09 |
| May 14 | Giants inform Yankees that the lease allowing them to play in the Polo Grounds will not be renewed at end of 1920 season |
| May 14 | Washington Senator Walter Johnson wins his 300th game vs Detroit |
| May 15 | Soccer team ADO '20 forms in Heemskerk |
| May 16 | Joan of Arc (Jean D'arc) canonized a saint |
| May 16 | Spanish bullfighter Joselito is fatally gored fighting his last bull |
| May 17 | 1st De Havilland double-decker flight (London) lands in Schiphol |
| May 17 | 1st flight by Dutch airlines KLM (Koninklijke-Luchtvaart-Maatschappij) |
| May 18 | 46th Preakness: Clarence Kummer aboard Man o' War wins in 1:51.6 |
| May 20 | Policemen raid the Cubs' bleachers and arrest 24 fans for gambling |
| May 23 | Pope Benedictus XV publishes encyclical Pacem Dei |
| May 27 | Tatar ASSR forms in Russian SFSR |
| June 1 | RKSV Volendam soccer team forms in Volendam |
| June 2 | Pulitzer prize awarded to Eugene O'Neill, Beyond the Horizon |
| June 4 | Peace of Trianon between Allies and Hungary |
| June 5 | 1st rivet driven on Bank of Italy headquarters at 1 Powell |
| June 5 | A's Vice President Thomas Shibe denies charges that baseballs are livelier |
| June 6 | General Wrangel opens offensive against red Army |
| June 8 | Reds' Edd Roush falls asleep in center during long infield argument Heinie Groh goes to wake him, but ump ejects Roush for delay of game |
| June 11 | Republicans nominate Warren G Harding for president |
| June 12 | 52nd Belmont: Clarence Kummer aboard Man o' War wins in 2:14.2 |
| June 12 | Farmer Labor Party organized, Chicago |
| June 15 | De Zweef soccer team forms in Nijverdal |
| June 17 | Dutch 2nd Chamber accept Anti-revolution law |
| June 20 | Yankees win protest of 1-0 White Sox win and game is replayed |
| June 24 | Chuvash Autonomous Region forms in RSFSR |
| June 25 | League of Nations places International head of Justice in Hague |
| July 1 | Washington Senator Walter Johnson no-hits Boston Red Sox, 1-0 |
| July 3 | 40th Wimbledon Mens Tennis: Bill Tilden beats Patterson (26 63 62 64) |
| July 3 | Java Technical School Bandung opens |
| July 3 | Royal Air Force holds an air display at Hendon, England |
| July 6 | Yankees score 14 in 5th inning and beat Washington Senators, 17-0 |
| July 10 | Tris Speaker is stopped at 11 consecutive hits by Tom Zachary |
| July 12 | Lithuania and U.S.S.R. sign peace treaty, Lithuania becomes independent rep |
| July 15 | Ruth ties his record of 29 home runs in a season |
| July 16 | 15th Davis Cup: USA beats Australasia in Auckland (5-0) |
| July 16 | China joins the League of Nations |
| July 16 | General Amos Fries appointed 1st U.S. Army chemical warfare chief |
| July 16 | Ruth sets season home run record with 30 en route to 54 |
| July 20 | Heerenveen soccer team forms |
| July 23 | British East Africa renamed Kenya and becomes a British crown colony |
| July 25 | Red Sox turn triple-play, but Ruth's 35th HR leads Yankees to 8-2 win |
| July 27 | Radio compass used for 1st time for aircraft navigation |
| July 27 | Resolute beats Shamrock IV (England) in 14th running of America's Cup |
| July 29 | 1st transcontinental airmail flight from New York to SF |
| July 29 | Mexican rebel Pancho Villa surrenders |
| August 1 | Papendrecht soccer team forms |
| August 1 | Peace of Riga-Independence of Latvia |
| August 2 | Marcus Garvey presents his "Back To Africa" program in New York City |
| August 8 | Tigers beat Yankees 1-0 in shortest AL game, 73 minutes |
| August 9 | Bulgarian and allied Peace of Neuilly-sur-Seine goes into effect |
| August 10 | Allies recognize Poland, Czechoslovakia and Romania |
| August 10 | Treaty of Sevres (Allies and Turkey) |
| August 10 | Turkish Government renounces its claim to Israel, recognizes British mandate |
| August 11 | 1st peace of Riga-Soviet Union recognizes Independence of Latvia |
| August 13 | 24th U.S. Golf Open: Ted Ray shoots a 295 at Inverness Club in Ohio |
| August 14 | Little Entente formed by Czechoslovakia and Yugoslavia |
| August 14 | Olympic Games open in Antwerp |
| August 16 | Ray Chapman, of Indians is hit in head by Yankees' Carl Mays pitch; he dies next day, only major league fatality |
| August 17 | In memory of Ray Chapman (died Aug 16), Yankees cancel game with Indians |
| August 18 | 1st class debut of Walter Hammond |
| August 18 | Tennessee ratifies 19th Amendment, guarantees women voting right |
| August 20 | 1st U.S. coml radio, 8MK (WWJ), Detroit began daily broadcasting |
| August 20 | Allen Woodring wins Oympic 200 m dash wearing borrowed shoes |
| August 20 | Israel publishes it's 1st medical journal "Ha-Refuah" |
| August 20 | Preliminary meeting in Akron to form American Pro Football League |
| August 20 | Red Sox-Indians game postponed in Boston to allow Indian players to attend Ray Chapman's funeral in Cleveland |
| August 21 | 3rd PGA Championship: Jock Hutchison at Flossmoor CC Flossmoor Ill |
| August 23 | M R Rinehart and A Hopwood's "Bat," premieres in New York City |
| August 25 | 1st U.S. woman to win in Olympics (Ethelda Bleibtrey) |
| August 26 | 19th amendment passes - women's suffrage granted |
| August 26 | Percy Fender (Surrey vs. Northants) scores 100 in 35 minutes |
| August 28 | 19th amendment acknowledges women's rights |
| August 31 | Belgium starts paying old age pensions |
| August 31 | Detroit radio station is 1st to broadcast a news program on the air |
| September 1 | France creates Lebanon |
| September 1 | New townhall of Rotterdam opens |
| September 2 | W Somerset Maugham's "East of Suez," premieres in London |
| September 4 | Last day of Julian civil calendar (in parts of Bulgaria) |
| September 5 | Iron monument unveiled at Stone churches, Flanders |
| September 6 | 40th U.S. Mens Tennis: Wm Tilden beats Wm M Johnston (61 16 75 57 63) |
| September 6 | Jack Dempsey KOs Billy Miske in 3 for heavyweight boxing title 1st radio broadcast of a prizefight |
| September 8 | U.S. Air Mail service begins (New York City to San Francisco) |
| September 12 | 7th Olympic games close in Antwerp Belgium |
| September 16 | Bomb explosion in Wall Street, kills 30 |
| September 17 | Cards set a record of 12 consecutive hits in 4th (10) and 5th (2) innings |
| September 17 | National Football League organizes in Canton Ohio 12 teams pay $100 each to join American Professional Football Association |
| September 22 | Chicago grand jury convenes to investigate charges that 8 White Sox players conspired to fix the 1919 World Series |
| September 23 | Alexander Millerand elected president of France |
| September 25 | 34th U.S. Womens Tennis: M B Mallory beats M Zinderstein (63 61) |
| September 25 | Vern Bradburn of Winnipeg Victorias kicks 9 singles in a game |
| September 28 | 8 White Sox indicted, threw 1919 World Series (Black Sox scandal) |
| September 28 | Dirk Fock appointed as Governor-General of Netherlands Indies |
| September 29 | Babe Ruth sets then home run season record at 54 |
| September 29 | Belgium annexes Eupen/Malmedy |
| September 29 | Joseph Horne Company in Pittsburgh sells radios for $10 |
| September 30 | Time Square Theater opens at 217 W 42nd St. New York City |
| October 1 | Dutch law provides for an 8 hour working day |
| October 2 | Only tripleheader of century (Reds win 13-4, 7-3 then Pirates win 6-0) |
| October 3 | Browns 1st baseman George Sisler gets his record 257th hit of season |
| October 3 | NFL (then American Pro Football Association) plays 1st games |
| October 6 | 1st brothers oppose each other in World Series, Cleveland's Wheeler Johnston pinch-hits as brother Jimmy plays 3rd base for Bkln |
| October 9 | 1st World Series game in Cleveland, Indians win 2-1 |
| October 10 | 1st Grandslam in WS (Smith) and 1st unassisted triple play (Wambsganss) |
| October 10 | Indian Bill Wambsganns makes 1st unassisted World Series triple play |
| October 10 | Indian's Elmer Smith hits 1st World Series grand slam |
| October 10 | Indians' Elmer Smith hits baseball's 1st post-season grand slam |
| October 10 | Italy annexes South Tirol (Alto Adige) |
| October 10 | Phoenix Cardinals (then in Chicago) play 1st NFL game, a 0-0 tie |
| October 12 | Cleveland Indians beat Brooklyn Dodgers, 5 games to 2 in 17th World Series |
| October 12 | Construction begins on Holland Tunnel connecting New Jersey and New York City |
| October 12 | Man O'War's last race and win |
| October 12 | Soccer team Quick '20 forms |
| October 13 | World Series celebration in Wade Park brings out 50,000+ Clevelanders |
| October 14 | Part of Petsamo province ceded by Soviet Union to Finland |
| October 17 | Chicago Bears (as Decatur Staleys) play 1st NFL game, win 7-0 |
| October 20 | "1st Year" with Frank Craven premieres in New York City |
| October 23 | Chicago grand jury indicts Abe Attell, Hal Chase, and Bill Burns as go-betweens in Black Sox World Series scandal |
| October 27 | League of Nations moves headquarters in Geneva |
| October 27 | Westinghouse radio station in East Pittsburgh, KDKA begins |
| October 29 | Ed Barrow appointed General Manager of New York Yankees |
| October 31 | Romania annexes Bessarabia |
| November 1 | Eugene O'Neill's "Emperor Jones," premieres in New York City |
| November 1 | Warren Harding elected 29th president |
| November 2 | KDKA (Pittsburgh) goes on air as 1st commercial radio station |
| November 2 | Warren G. Harding elected president |
| November 3 | "Emperor Jones" opens at Provincetown Theater |
| November 8 | Actress Edna Lewis Thomas debuts at Putnam Theatre Brooklyn |
| November 8 | Baseball meeting to depose Ban Johnson is set for Nov 12th |
| November 10 | George Bernard Shaw's "Heartbreak House," premieres in New York City |
| November 12 | Judge Kennesaw Mountain Landis elected 1st baseball commissioner |
| November 13 | Hudson River frozen at Albany |
| November 14 | American Pro Football League's Chicago Tiger Joe Guyon punts 95 yards |
| November 15 | Ernst Toller's "Massen und Menschen," premieres in Neurenberg |
| November 15 | Free City of Danzig forms under League of Nations protection |
| November 15 | League of Nations holds 1st meeting, in Geneva |
| November 16 | 1st postage stamp meter is set in Stamford Connecticut |
| November 18 | Apollo Theater (Academy, Bryant) opens at 221 W 42nd St. New York City |
| November 20 | Nobel Peace Prize awarded to U.S. president Woodrow Wilson |
| November 21 | Karel Capek's "Vec Makropulos," premieres in Prague |
| November 21 | Mussolini's squad begins terror, 11 die in Bologna Italy |
| November 25 | 1st Thanksgiving Parade in Philadelphia |
| November 25 | WTAW of College Station, Tx, broadcast 1st football play-by-play |
| December 3 | Turkey and Armenia agree to peace treaty |
| December 4 | 1st Pro football playoff game Buffalo-7, Canton-3 at Polo Grounds |
| December 4 | 8th CFL Grey Cup: University of Toronto defeats Toronto Argonauts, 16-3 |
| December 5 | Pro football playoff game Akron and Buffalo 0-0 tie, title undecided |
| December 7 | NSW make 802 against South Australia, then Mailey takes 8-81 |
| December 7 | USPD-KPD parties merge into Vereinigte Communist Party of Germany |
| December 12 | Maurice Ravels ballet "La Valse," premieres in Paris |
| December 13 | F Pease's interferometer measures 1st stellar diameter (Betelgeuse) |
| December 13 | League of nations establishes International Court of Justice in The Hague |
| December 13 | Netherland breaks contact with kingdom of Serbia, Croatia and Slavia |
| December 14 | Heavyweight Jack Dempsey KOs Bill Brennan in New York City |
| December 14 | Jack Dempsey KOs Bill Brennan in 12 for heavyweight boxing title |
| December 16 | 8.6 earthquake destroys 15,000 miles (Kansu China); Over 180,000 die |
| December 17 | AL votes to let spitball pitchers to continue using it |
| December 17 | British Empire receives League of Nations mandate to Nauru |
| December 17 | Japan receives League of Nations mandate over Pacific islands |
| December 17 | South Africa receives League of Nations mandate over SW Africa |
| December 18 | 1st U.S. postage stamps printed without the words United States or US |
| December 19 | 1st U.S. indoor curling rink opens (Brookline, Mass) |
| December 20 | Bert Collins scores 104 on Test Cricket debut vs. England SCG |
| December 20 | Bob Hope became an American citizen |
| December 21 | Jerome Kern/BG DeSylva's musical "Sally," premieres in New York City |
| December 23 | Ireland divided into 2 parts, each with its own parliament |
| December 23 | King George V signs Home Rule Act |
| December 24 | Enrico Caruso gives his last public performance (New York City) |
| December 29 | The netherlands/Venezuela recover diplomatic relations |
| December 29 | Yugoslav government bans Communist Party |
| December 31 | Roy Park makes 1st-ball duck in only Test Cricket India, vs. England at MCG |
