More like two-thirds
Civil War Casualties
Casualties Numbers And Battle Death Statistics For the American Civil War
Though the number of killed and wounded in the Civil War is not known precisely, most sources agree that the total number killed was between 640,000 and 700,000.
Union Civil War Casualties
Combat Deaths: Over 110,000
Other Deaths*: Over 250,000
Confederate Civil War Casualties
Combat Deaths: Over 95,000
Other Deaths*: Over 165,000
(*Other Deaths include, among others: disease (by far the most common cause of death), accidents, drowning, heat stroke, suicide, murder, execution.)
http://www.historynet.com/civil-war-casualties