To repeat a question that was deleted from Ask Reddit. When I was younger I read that 700+K Americans died in WWII. Years later it dropped to 600+K and then down to 500+K. Watching a documentary on Reddit today they said 400+K. Of course it can be hard figuring this, misreports, dual reports, and men dying years after they were wounded due to their wounds. How many do you think died?
The US Department of Veteran's Affairs says the total was 405,399:
Battle Deaths 291,557
Other Deaths in Service (Non-Theater) 113,842
The National WWII Museum gives slightly different numbers, and also includes civilian deaths. They say there were 416,800 military deaths and 418,500 military and civilian deaths.
I'm afraid I don't know why there is a discrepancy between the two. I would probably trust the VA for more accurate figures. I don't know if there is any 'official' source for civilian deaths.