Figure 7. More Illinois soldiers, this time Company F of the 7th Illinois atop Lookout Mountain in June 1864. Both 11 button and 9 button shell jackets are in evidence (from Echoes of Glory, pg.124)
In Table 1, I list all dated large group images in which I have been able to identify shell jackets. As stated previously, New York shell jackets have been demonstrated in use throughout the war. However, Schuylkill shells are hard to document before 1863 and the use of Illinois/Ohio state jackets can not yet be documented before 1864. This also holds true for datable CdV images. The reason for this delay may be that they are simply replacing the use of more expensive frock coats in some units. More image archives will need to be searched to arrive at firmer guidelines, although it appears safe to say that shell jacket use by Federal infantrymen from Illinois and Ohio (and other units serving in the West) was fairly common in the last two years of the war.