Sherman called it was the bloodiest battle on the continent, in terms of numbers involved. Perhaps his statement should be examined. The 7th Illinois appears on this list, but note that several Federal regiments in the east reported higher casualty percentages.
http://www.civilwarhome.com/foxschapter3.htm

Of course this doesn't take into account Confederate casualties, which on the whole were twice the percentage of casualties reported by Federal sources.

By late 1864 Federal soldiers -- such as the men of the 7th Illinois Regiment -- often had the considerable advantage of being armed with high-quality repeaters, such as the Henry Rifle, and fighting behind well-prepared defenses. Confederates ordinarly used single-shot firearms.
http://www.rarewinchesters.com/articles/art_hen_07.shtml

Notice members of the 7^th Illinois with their Henry rifles:
http://members.tripod.com/~rjsnyder/7th.jpg

Confederate casualty rates would be significantly higher as a result of the disparity of arms, equipment and numbers. Confederate morale and motivation for fighting would be higher, since many were literally fighting to defend their homes and families. Federal soldiers had no such motivation.