- Oct 1 Dutch law provides for an 8 hour working day
- Oct 1 Sir Percy Cox landed in Basra to assume his responsibilities as high commissioner in Iraq.
- Oct 2 Cincinnati Reds and Pittsburgh Pirates play first and only MLB triple header in the 20th century; Reds win the first two games, 13-4 and 7-3; Pirates avoid the sweep in the finale, 6-0
- Oct 2 The Chinese sign an agreement with the Russo-Asiatic Bank, largely French and Russian controlled, which will oversee the Chinese Eastern Railway, but give local supervision to China
- Oct 3 American Pro Football Association (later the NFL) plays 1st full round of games; Dayton Triangles beat Columbus Panhandles, 14-0 in first official game at Triangle Park, Dayton
- Oct 3 St Browns 1st baseman George Sisler collects his 257th hit of the season to set MLB record that lasts until the 21st century.; Browns beat White Sox, 16 - 7
- Oct 6 1st brothers oppose each other in World Series, Cleveland's Wheeler Johnston pinch-hits as brother Jimmy plays 3rd base for Brooklyn
- Oct 10 Cleveland Indians outfielder Elmer Smith hits baseball's first ever World Series grand slam and teammate Bill Wambsganss makes the 1st unassisted World Series triple play (Game 5)
- Oct 10 Italy annexes South Tirol (Alto Adige)
- Oct 10 Phoenix Cardinals (then in Chicago) play 1st NFL game, a 0-0 tie
- Oct 12 Baseball World Series: Cleveland Indians beat Brooklyn Robins, 8-1 at League Park for a 5 games to 2 series victory; Indians first Championship
- Oct 12 Construction begins on Holland Tunnel connecting NJ & NYC
- Oct 12 Man O'War's last race & win
- Oct 13 World Series celebration in Wade Park brings out 50,000+ Clevelanders
- Oct 14 Part of Petsamo province ceded by Soviet Union to Finland
Poor Little Ritz Girl
Oct 16 Sigmund Romberg and Alex Gerber's musical "Poor Little Ritz Girl", with additional songs by Richard Rodgers and Lorenz Hart (marking their Broadway debut), closes at the Central Theatre, NYC, after 93 performances
- Oct 17 Decatur Staleys, later known as Chicago Bears, play 1st American Professional Football Association game against an affiliated APFA team; beat Rock Island Independents, 7-0 at Douglas Park, Rock Island, Illinois
- Oct 20 "1st Year" with Frank Craven premieres in NYC
- Oct 23 African demonstrators shot in Port Elizabeth, South Africa
- Oct 23 Chicago grand jury indicts Abe Attell, Hal Chase, & Bill Burns as go-betweens in "Black Sox" 1919 World Series Baseball scandal
- Oct 27 League of Nations moves headquarters in Geneva
- Oct 27 Westinghouse radio station in East Pittsburgh, KDKA is granted a Limited Commercial license by the Department of Commerce
- Oct 29 Ed Barrow appointed GM of NY Yankees
- Oct 30 The Communist Party of Australia is founded in Sydney.
- Oct 31 Romania annexes Bessarabia
Admirals
Aviators
Gangsters
Generals
Industrialists
Suffragists