The claim: Rantoul, near Champaign/Urbana - This closed base had WWII - era barracks that were condemned and torn down, but the medical facility was upgraded and additional fencing put up in the area. More info needed.
What it really is: The base was closed in 1993, but many of the buildings were converted into civilian and commercial use, from light manufacturing, to retirement communities.
The former base also includes a museum called the Octave Chanute Aerospace Museum.
As for the actual claim about the hospital, well, hospitals tend to be expanded to accommodate the population, therefore it is necessary to construct new additions to a hospital, and because construct sites tend to be dangerous places (and has equipment that tends to get stolen) it is necessary to put fencing up around such a site.
The only military presence left at the site is a youth boot camp for troubled youths ages 16 to 18 called the Lincoln's ChalleNGe Academy that is run by the Illinois National Guard and Air Guard.