These company rosters are comprised only of those men of the Third Michigan Infantry, first organization, which served in the Army of the Potomac from June of 1861 until June 1864 when it was consolidated with the Fifth Michigan Infantry.

The "reorganized" Third Michigan, which served in the southwestern theater of the war from the fall of 1864 until the spring of 1866, was an entirely seperate unit altogether.

Company A
Company B
Company C
Company D
Company E
Company F
Company G
Company H
Company I
Company K
Staff
Unassigned