The Sheraton hosted Windycon, Capricon, and Duckon at various times (and under various names). Capricon would probably still be there if the owners hadn't decided to build the water park. This ate a big chunk of the con's function space and caused the owners to not want to host the con so that they could rent those rooms to people who wanted to stay at the hotel and go to the water park.
I predicted that those people didn't really exist -- that anyone who was motivated enough to stay in the hotel overnight would go up to the water park near Gurnee Mills where one or the other parent could spend time shopping and where there are numerous restaurants to eat at. I may have been completely correct or it may just have been the recession taking the air out of the scheme.
I suspect that someone will eventually reopen the facility, because it's more valuable as a hotel and water park than it is as vacant land. But not right now.