NPS CWS&SS shows:

Charles I. Miller
Regiment Name 8th Ohio Infantry (3 Months, 1861)
Side Union
Company D
Soldier's Rank_In Pvt.
Soldier's Rank_Out Pvt.
Film Number M552 roll 74

Note: middle initial is shown as "I" not "R".

8th Regiment, Ohio Infantry (3 months, 1861)
Organized at Cleveland, Ohio, April 18-May 4, 1861. Moved to Camp Dennison, Ohio, and duty there till June 22. Reorganized for three years June 22, 1861. Three-months men mustered out July 24, 1861.

Others of that surname in the unit:

Soldier Name
Company Rank In Rank Out

Miller, Abraham
Co A Pvt. Pvt.

Miller, Andrew
Co A Pvt. Pvt.

Miller, Daniel
Co G Corpl. Corpl.

Miller, Henry
Co I Pvt Pvt

Miller, James L.
Co F Pvt Pvt

Miller, Peter
Co K Pvt Pvt

Miller, Peter A.
Co D Pvt Pvt

Miller, Truman D.
Co H Pvt Pvt

Miller, Wells W.
Co E Sgt Sgt

Miller, William
CO K Pvt Pvt