Good evening all,
Being a resident of the south suburbs of Chicago, I can offer a little advice on some areas for train watching.
If you like yard operations, you can't beat CN's massive yard in Homewood, IL. Easy to get to from downtown via Metra's Electric District, which stops right next to the entrance to the yard. Amtrak also stops here too, plus there are a few run through freights that pop up now and then. On display on the other side of the tracks is an old IC GP10 and an IC caboose. The neighborhood is great, and I've had no troubles here.
Also accessible via Metra Electric is the train watching platform in Matteson, IL. This is only a few miles south of Homewood. This is home to CN's cloverleaf junction that connects the old IC main with the old EJ&E. It is very impressive to watch a train work its way through here. Also on site here is a restored EJ&E caboose. As with Homewood, this area is pretty safe as well.
Blue Island Junction does have a lot of freight action, but I personally wouldn't go there, even in the daytime. I've had to deal with CSX police here and a disgruntled tower operator who insisted I was trespassing, even though I was standing on the sidewalk next to the street.
Joliet during the day is O.K., but Joliet Union Station just recently closed and all passenger operations have been moved to new platforms. It sound's like there will be some new track alinement going on here. Though I haven't been her since the closure, from what I've heard the old platforms have been fenced off, and sight lines from the new platforms aren't that great.
If a high volume of trains is your thing, a good alternative spot to Joliet is in Lockport, IL. I've been here day and night with no problems. This is the BNSF Chillicothe Sub, and the sweeping curve under the 9th street bridge makes for some great photos. Bring a lawn chair if possible.
Downtown wise, I've struck out at the Canal Street crossing, though I went on a weekend. A weekday visit would probably yield good results. Another good spot downtown is the Roosevelt Street Museum Campus station. This is Metra Electric and the South Shore Line, and trains are frequent.
This is all that I can think off at the moment, any questions feel free to ask.
Josh