This is either a gg-grandfather or gg-uncle on my father's side of the family. He is almost certainly from an Illinois Regiment. But Iowa, Ohio, and Pennsylvania are possible long shots.
Answers that can help me solve the identity --
- Anything else!
Soldier in image has light eyes (in addition to being older - mid-20s to 30?)
Depending on the quality of Regimental records, physical descriptions were recorded.
The same for pension records.
"Light eyes" will be one confirming data point.