My Great Grandfather Norman Flanigan served for another (probably paid). He was 14 years old and was captured and spent some time as a P.O.W. There is some information that he was at Camp Douglas, near Chicago. His home is near Raymond in Hinds County and is in good repair and occupied.
The widow's application for a pension mentions other units but I don't know how reliable the information is.
I was able to spend a couple of days researching in Missippi a few years ago.
I found Norman Flannigan & family's graves but I haven't found my Great Grandfathers grave. His name was Benjamin Franklin Alexander.