The Land of Oz theme park in NC isn't abandoned. It opens seasonally for a few weekends at a time. It's not a full-on park experience, but it's not abandoned
Large chunks of Ft Ord in CA are still abandoned and kind of neat for an urban explorer. Some parts are still in use by the military, but others - especially the older housing areas and temporary training barracks that don't meet earthquake codes - are awaiting demolition.