I had two family members in the 45th Illinois.

1st Lt-Thomas J. Prouty company B
Pvt Elijah Prouty also of company B

They were brothers. I checked the other Illinois regiments you mentioned, there were no "Prouty's" in those regiments.

Prouty's in Illinois regiments:
Had 3 in the 27th Illinois--Father, Son and another Son.
32nd, 36th, 45th, 52nd, 65th and the 92nd Illinois.

In the 52nd Illinois, two brothers were in the same company "I" (George E. Prouty and Addison Prouty)

11 Prouty's served in Illinois regiments. There are more but they are not listed in the national archives website, but are on our genealogy book.

Shawn