Not since 1945, but...
US territory was invaded and occupied in 1942. Two of Alaska's Aleutian Islands (Attu and Kiska) were invaded an occupied by the Japanese.
There was also the US territory of Wake Island that was invaded by the Japanese in 1941.
And lest we forget, the Philippines and Guam were also US territories (the same as Puerto Rico) during WWII. Both were invaded and occupied by the Japanese during the war. In the Philippines, tens of thousands of civilians were slaughtered by the Japanese. Untold thousands more were imprisoned (including my later father-in-law).
Other US territory was attacked but not invaded during WWII, including Pearl Harbor and Midway.