“For 110 years, the numbers stood as gospel: 618,222 men died in the Civil War, 360,222 from the North and 258,000 from the South — by far the greatest toll of any war in American history.
But new research shows that the numbers were far too low.”
The new number, fairly well reasoned, is 750,000.
an article from the NY Times worth reading:
Civil War Toll Up by 20 Percent in New Estimate – NYTimes.com.