You will probably need to rent a car. The regional train, METRA, runs to Zion which is close to the conference center, but there is no car rental available at the train station. It's a little over an hour by train, but it doesn't make a difference if you can't get to Illinois Beach regardless. Maybe you could check out cabs or an uber/lyft once you reach Zion if you do select the train, but I would have transportation reserved before you arrive in Zion.
I didn't know there were any previous reviews missing, but I suspect they are gone because this resort has been through a year of total upgrading and remodeling. And the only reason I know this is because my husband and I had a chance to talk to the manager about it. I was at the hospital one day and mentioned to a nurse that I was staying at the resort. She commented that it would be nicer if it weren't so "dingy" and if the food was better. I was like, huh? The place is spotless with new carpeting, wall paper, paint, beds, bedding, pillows and all kinds of amenities, so I couldn't figure out what the nurse meant. And the food is literally to die-for, from breakfast to dinner. I told her that, and she seemed pleasantly surprised. The next morning when the manager came by and asked how we liked our breakfast, I shared with him what the nurse had said. That's when he told us he had spent over a year remodeling this hotel, top to bottom, inside-out. They even redid the pool, which he said had been taken out in a tornado a couple years earlier. So, in answer to your question, now that this resort is such a fine place to be, and obviously NOT the same resort it was a year ago, I would say it would be only fair to remove older reviews that reflect experiences with the old hotel.