Hmmm. Your use of the word Killed bothers me. The DEATH rate was near 25 percent, but 2/3 of those died of disease.
http://www.digitalhistory.uh.edu/historyonline/us20.cfm
1 out of every 4 soldiers were killed in the civil war?
2 answers
This site will give you the numbers of casualties and the number of soldiers on each side.
http://www.civilwarhome.com/casualties.htm
http://www.civilwarhome.com/casualties.htm