As a wild guess probably a doxen or less in the USA and say, ?1000 or so overseas -as we had a habit of 'getting when the getting was good'
However, we also had the US Merchant sailors and the 'runs to Murmask' etc. along with other nations of course. So the US civilians did a good job and were luckier than other allied nations. Many a 'Rosie the Riveter' help greatly in the US etc. Some died - say the ladies who ferried B-17s to Europe and, sadly, didn't make it for various reasons.