The Jewish population in 1860 has been estimated at about 200,000. There were about 8,000 Jewish-Americans in the Union and Confederate armies: approx. 3000 for the South and 5000 for the North (proportional to the population that settled in these regions).
What has always fascinated me about the Civil War is that it was one of the very few wars in history in which Jews fought on both sides.
Rumours persist that anti-Semitism was far greater in the North than in the South and that many Union commands would not knowingly admit Jews into their ranks.