- Sep 1 Bulgaria government of Bagrjanow, resigns
- Sep 2 Belgium's Emissie bank closes
- Sep 2 Future US President George H. W. Bush bails from a burning plane during a mission in the Pacific
- Sep 2 US leaders meet in Belgium
Last Dutch Jews to Auschwitz
Sep 3 68th and last transport of Dutch Jews (including Anne Frank) from Westerbork leaves for Auschwitz concentration camp
- Sep 3 Canadian troops liberate Abbeville, France
- Sep 3 French troops liberate Lyon
- Sep 3 Holocaust diarist Anne Frank sent to Auschwitz concentration camp [1]
- Sep 3 Prince Bernhard appointed supreme commander of Netherlands Domestic Armed Forces
- Sep 3 Tank division of British Guards free Brussels
- Sep 4 2,087 Jews transported for Westerbork to KZ-Lower Theresienstadt
- Sep 4 British 11th Armoured Division frees Antwerp
- Sep 4 Finland breaks diplomatic contact with Nazi Germany
- Sep 4 US 1st Army frees Namur, Belgium
- Sep 4 US National Championship Men's Tennis, Forest Hills, NY: American Frank Parker wins 1st of 4 Grand Slam titles; beats William Talbert 6-4, 3-6, 6-3, 6-3
- Sep 4 US National Championship Women's Tennis, Forest Hills, NY: Pauline Betz Addie wins her third straight US title; beats Margaret Osborne 6-3, 8-6
- Sep 5 "Mad Tuesday" 65,000 Dutch nazi collaborators flee to Germany
- Sep 5 5 resistance fighter executed in Terneuzen, Netherlands
- Sep 5 Allies liberate Brussels
- Sep 5 Belgium, Luxembourg & Netherlands sign customs Unity treaty
- Sep 5 British Prime Minister Winston Churchill travels to Scotland
- Sep 5 Dutch Armed Forces forms, under prince Bernhard
- Sep 6 Gen Von Zangen's 15th army escape from Zealand
- Sep 7 SS-general Kurt Meyer takes Durnal, Belgium
- Sep 7 Strongest Hurricane of century in Netherlands (wind force 12)
- Sep 8 1st V-2 rockets land in London & Antwerp
- Sep 8 Russians march into Bulgaria; Bulgaria declares war on Germany
- Sep 9 Allied forces liberate Luxembourg
- Sep 9 Red Army supports coup in Bulgaria, instituting new Communist government (1946-1990) during the "National Uprising"
- Sep 9 Resistance fighter Jaap Musch arrested in Nijverdal, Netherlands
- Sep 9 US 113th cavalry passes Belgian-Dutch borders
- Sep 10 Lieutenant-General Frederick Browning against Montgomery "But, sir, I think we might be going a bridge too far"
- Sep 11 A reconnaissance squadron of the US 5th Armored Division "Victory Division" is 1st allied force to enter Nazi-Germany
- Sep 12 Noorbeek becomes the first liberated community in the Netherlands during World War II
Second Quebec Conference
Sep 12 Second Quebec Conference: Franklin D. Roosevelt, Winston Churchill and the Combined Chiefs of Staff meet in Quebec City, Canada to discuss Allied occupation zones, the Morgenthau Plan, U.S. Lend-Lease aid to Britain and the role of the Royal Navy
- Sep 12 US Army troops enter Germany for 1st time
- Sep 13 30th Infantry division of US 1st Army frees Margraten
- Sep 13 Great Atlantic hurricane reaches peak intensity as a Category 4 storm, goes on to kill 300-400 along the US East Coast
- Sep 13 Last transport out camp Westerbork to Bergen Belsen
- Sep 13 US 28th Infantry division opens assault on Siegfried line/Westwall
- Sep 14 6,500 Dutch/Indonesian captives sent to Junyo Maru
- Sep 14 Great Atlantic hurricane hits New England, 300-400 die along the US East Coast
- Sep 14 Gulpen, Meerssen & Maastricht freed
- Sep 14 US 28th Infantry division occupies 1.5 km of Roscheid
- Sep 14 US 4th Ivy League Inf division pushes through Westwall
- Sep 15 British bombers hit German battleship Tirpitz with Tallboy bombs
- Sep 15 Soviet troops free Sofia, Bulgaria
- Sep 15 US 1st Infantry division pushes through to Westwall
- Sep 15 US 28th Infantry division occupies Hill 555 at Roscheid
- Sep 15 US troops land on islands of Palau and Morotai, western Pacific
Churchill's US Visit
Sep 17 British Premier Winston Churchill travels to US
- Sep 17 Dutch begin railroad strike against German occupiers
- Sep 17 Operation Market Garden: In the largest airborne operation of WWII, Allied paratroopers land in the Netherlands in a failed attempt to capture the Arnhem bridge over the Rhine
- Sep 18 WWII: British submarine Tradewind torpedoes Junyo Maru: 5,600 killed, including 1,377 allied POWs and 4,200 Javanese slave laborers
- Sep 18 WWII: Eindhoven, Netherlands freed by American and British troops (Lightly Day)
- Sep 18 WWII: US 266th division defeats German troops at Brest Bretagne in Brittany, France after a 7 week siege; 37,000 prisoners taken, ports rendered useless
- Sep 19 Armistice between Finland and Soviet Union is signed. (End of the Continuation War)
- Sep 19 Luftwaffe bombs Eindhoven: 200 killed
- Sep 20 Nijmegen is liberated from German occupation
- Sep 20 Polish forces liberate Terneuzen in the Netherlands
- Sep 21 Operation Market Garden: Last British paratroopers at Arnhem Bridge surrender after several days of fighting
- Sep 21 Operation Market Garden: Polish paratroopers land at Driel after a delay due to bad weather and a shortage of planes
- Sep 22 Boulogne reoccupied by the Allies
Martial Law in the Philippines
Sep 22 President Jose P. Laurel declares the Philippines under martial law in 1944 through Proclamation No. 29
- Sep 22 US troops land on Ulithi atoll, western Pacific
- Sep 23 Proclamation No. 30 was issued, declaring the existence of a state of war between the Philippines and the United States and the United Kingdom
- Sep 25 Operation Market Garden ends in Allied failure as the last British and Polish paratroopers are evacuated from Oosterbeek, near the town of Arnhem
- Sep 26 Soviet forces occupy Estonia
- Sep 26 World War II: Battle of Arnhem ends in Allied failure as German forces link up on both sides of the Lower Rhine river and mop up last British resistance
- Sep 27 Dutch cities Helmond and Oss are liberated
- Sep 28 1st TV Musical comedy (The Boys from Boise)
- Sep 28 Nazi forces begin killing civilians in the Italian village of Marzabotto
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