Laura,
My first post was just on those units raised near here at Corinth. There were 10 other Mississippi units that fought for the Union, nine of which were of African Descent. They were the 1st MS Cav, 1st MS Heavy Artillery, 2nd MS Heavy Artillery, and the 1st through 6th MS Infantry. The only white unit was the 1st Mississippi Mounted Rifles.
This info is from Dyer's Compendium.
Tom