Obviously being central Illinois, there is no signature scenery (like, say, Tehachapi). My first thought, then, would be to focus on signature structures, especially ones still there so you can get current pix for modeling purposes. For example, the towers at Pana and Ramsey still exist despite having been long abandoned by the railroads; for that matter the rails in Ramsey have been gone for a couple of decades. There's nothing old in Effingham (city), sadly - nearly everything anywhere near the diamond was razed when they put in the double overpass for US40 and 45.
EDIT: Speaking of signature structures, while not railroad-related, the two-story outhouse in Gays, IL has been preserved,
http://www.jldr.com/2storyohgaysillinois.html. Gays is in your modeling area, but I think it was on the Big Four.