I had planned on visiting the Armstrong Bridge last Fall when I was in Danville. Unfortunately, due to time constraints, I wasn't able to. I hope they plan to leave this beauty alone.
It is shame to hear the other bridge is being replaced. I have not visited it, but based on aerial images and NBI data I suspect the smaller bridge is a concrete through girder bridge. I made a page for it in case anyone got any photos before it was demolished. https://bridgehunter.com/il/vermilion/bh89882/
This bridge is temporarily closed for summer 2020 as the smaller creek bridge south of it is being replaced.
This is a beautiful example of an Attica Bridge Co. span, that looks to be well preserved. I changed the truss type to a Warren, but couldn't tell from the photos if it was riveted or bolted.
I have it marked on the agenda on an upcoming 4 day trip to this area 04/21. Will have an update.