Was Alaska ever invaded?

Three of the Alaskan islands were invaded and actually occupied by a large force of Japanese for well over a year. The US services lost thousands of soldiers in the battles, and to the weather, to reclaim them. On one island, several hundred Japanes even committed suicide to avoid capture.

So yes, the US has been attacked, has had a foreign force occupy land and has had foreign soldiers die in battle on its land.

Battle of the Aleutian Islands See the related website for the story of the invasion and re-taking of these islands.