David,
It's really not at all odd that his unit would not have been in the Battle of Iuka. Units were assigned where the authorities decided there was a need, not necessarily based on proximity to their homes. In the case of the 26th Mississippi, the entire regiment was captured at Fort Donleson in Tennessee in February of '62, with the enlisted men being imprisoned at Camp Morton in Indianapolis. They were not exchanged until Sept. 13th at Vicksburg, just 6 days before the Battle of Iuka. It would take several days, if not weeks, for the unit to be reassembled at Jackson. They were then sent to Holly Springs, but this was after the Second Battle of Corinth in October.