The claim: Jacksonville, ?
What it really is: Naval Air Station Jacksonville is a military airport, and is actually one of two naval bases located in Duval County, Florida.
All the buildings located there are basically what would be typically expected at a facility that was both an airport and a military air base. Also, there are multiple civilian facilities surrounding the base (including houses and businesses). It would be highly unlikely that a prison camp could be hidden there for very long without a lot of people seeing it.