If you are visiting Hersheypark and visit ZooAmerica...your admission into the zoo is free (on the same day). If you want to just visit the wildlife park then admission is $11.00 for adults, $9.00 for children ages 3 and over. Children under the age of 3 are free with a paying adult.
When we first walked in we entered the admission entrance building and paid for our admission and obtained a free wildlife park map. I highly suggest you grab the map so you can find your way around, although the zoo has great signage to help direct you. There are public restrooms in this building, so use them before you enter the zoo.
The ZooAmerica - North American Wildlife Park is open year round but their hours do vary according to the season. You will want to check out their web site before you go to see their hours of operation and if they have any special events going on at that time. Have fun!