- Sep 1 Jerome Travers establishes a US Amateur Golf Championship record by downing George Crump, 14 & 13, in a 1st-round match at the Country Club of Detroit in Grosse Pointe Farms, Michigan
- Sep 1 The German ambassador to the US pledges again that German submarines will no longer sink liners without warning and providing safety of passengers and crew following the sinking of the British liner "Arabic"
- Sep 5 Anti-war conference in Zimmerwald, Switzerland
Nicholas II Takes Command
Sep 5 Tsar Nicholas II, distressed by increasing Russian losses, assumes personal command of his nation's military forces; clearly a symbolic act and devastating for his leadership
US Men's Tennis Open
Sep 8 US National Championship Men's Tennis, Forest Hills, NY: William Johnston beats Maurice McLoughlin 1-6, 6-0, 7-5, 10-8 in first US event held at West Side Tennis Club, Forest Hills, New York
- Sep 9 Association for the Study of Negro Life and History formed in Chicago by Carter G. Woodson and others. Now the Association for the Study of African American Life and History.
- Sep 16 Tsar Nicholas II of Russia adjourns 4th Duma
- Sep 16 US takes control of customs & finances of Haiti for 10 years
First Appearance of Jeeves and Wooster
Sep 18 Jeeves and Bertie Wooster make their first appearance in P. G. Wodehouse short story "Extricating Young Gussie" published in "The Saturday Evening Post" in the US
Stonehenge
Sep 21 Cecil Chubb buys English prehistoric monument Stonehenge for £6,600
- Sep 21 Emanuel Querido ("Kerido") begins publishing Querido
- Sep 22 Boston Red Sox ask Boston Braves for use of Braves Field (10,000+ capacity) for Baseball World Series against Philadelphia Phillies
- Sep 22 Southern Methodist University in Dallas, Texas, holds its 1st class
- Sep 22 Xavier University, 1st Black Catholic College in US, opens in NO LA
- Sep 25 Battle of Loos commenced, lasted until 14th October. Chlorine gas deployed by the British was blown back into their own trenches: 59,000 British & 26,000 German casualties
- Sep 25 The Second Battle of Champagne begins with French offensive against German army (ends with French retreat 6 Nov)
- Sep 28 Battle of Kut-el-Amara: British defeat Turks in Mesopotamia
- Sep 29 1st transcontinental radio telephone message sent by U.S. naval radio station at Arlington, Virginia. to naval radio station at Mare Island, San Francisco
- Sep 29 British army conquers Chilly al Imara, Mesopotamia
- Sep 29 Dutch Opera's 1st performance
- Sep 29 Herbert/Blossoms musical "Princess Pat" premieres in NYC
- Sep 29 Hurricane claims 275 in Mississippi Delta
- Sep 29 Philadelphia Phillies clinch their 1st pennant
- Sep 30 Red Sox clinch AL pennant by beating Detroit
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