I used to see that bridge all the time back in my Illinois days. It sounds like a great discovery.
I have been researching my namesake Rossford Yard for years and I am still coming up with new, eh, old photos that I figured didn't exist. How much have you used the internet to search for info? Or the big library at University of Illinois in Champaign?
My guess is that for you, the floodgate of info is just starting and you will be having lots of fun with that bridge from here on out. Congrats!
Oh, I've been having fun with that bridge for quite a while now...

From March 2007:

To present:


I've done a ton of Internet research, along with my own "field trips" when I go back to visit my mother in Illinois at Christmastime. But Terraserver, and Bing Maps, and Google Earth, only show me what's there
now. That's the reason I was so excited about the Google Books find--it provided information about the history of the bridge that I hadn't been able to obtain up to that point.
I bought a book from the Kankakee Valley Historical Society about Kankakee-area railroads, but as I mentioned above, it turned out to be less useful than I'd hoped.
At your suggestion, I checked the online offerings of the U of I, but everything there is behind a students-only password wall except for the stuff that's sourced from Google--which I can get straight from Google.