Hershey's offer free trolley service to/from the parking lot. The area is so huge so make sure to remember the number you park your car. If not, you might find yourself roaming around and checking all the parked vehicles in the area.
Local public transportation
If you are arriving to the area by train or bus and want to get to the Hershey attractions consider riding the Capital Area Transit - CAT.
There are daily runs into Hershey from Harrisburg's downtown transportation center. The "322 Hershey" will take you there.
If you arrive by air into Harrisburg the local transportation options can be found here: http://www.flyhia.com/services/ground-transportation.asp
A project is underway at the airport that will link rail service with flights arriving at Harrisburg International Airport - HIA