When was it built?
Trying to guess a truss bridge age from photos is tricky. One of Murphy's law corollaries is that none of the photos will include what I want to see. *smiles* And as bridge technology advanced, not every building progressed at the same rate.
That said, it is pin-connected, thus probably prior 1925. The eye-bars are upset, which often means later than 1890. The lower joint pins are at the very bottom, which suggest older as does the knee-braced sway braces.
So, based only on what I can see from the limited detail of the pictures, I'd guess 1895 to 1910.
But that is pretty close to a _wild_ guess.
when was this bridge built?
I found an Illinois Central map for this area (Springfield Division), which lists the two similar IC bridges in this county as being built in 1890. Hope that answers any past questions.