Metra trains can be used to reach most hot spots. The Union Pacific West Line and the Burlington Northern Santa Fe line are filled with hot spots, with heavy freight traffic sharing those lines with Metra trains.
Chicago's ten best train watching sites, as selected a number of years ago by TRAINS Magazine staff members.
This zoomable Google Map has been marked with the "Top Ten" railfan spots in the Chicago area. Also marked are the most useful public transportation transfer locations, for getting to and from these locations. When zooming in close enough on Google Maps, all train station and bus stops are marked as little blue squares, which can be clicked for route and schedule information.
Link to a Web site containing more comprehensive information, on where to watch trains in the Chicago area.
Train Watcher's Guide To Chicago
John Szwajkart's Web Site includes information on ordering his book, "Train Watcher's Guide To Chicago", which has been the standard reference book for Chicago railfanning for more than 30 years. Similar books are available for St. Louis and Kansas City.