Was any part of the current 50 states of the US occupied by the Japanese during the Second World War?
Part of Alaska was occupied (although of course Alaska did not have statehood at that time). This occupation involved the Aleutian islands, when Attu and Kiska were invaded on 3 June 1942 by Japanese forces in order to divert American forces away from the main Japanese attack at Midway Atoll. The U.S. Navy, having broken the Japanese naval codes, concluded that this was just a diversion, and it did not expend large amounts of effort in defending the islands. More than 90 Americans were taken to Japan as prisoners of war. Most of the civilian population (over 800) of the Aleutians and Pribilovians were interned by the United States in camps in the Alaska Panhandle. During the Aleutian Islands Campaign, American and Canadian forces invaded Japanese-held Attu and defeated the Japanese, and subsequently regained control of all the islands (15 August 1943).