The BNSF Metra line has a stop half a mile from the zoo. Get off at the Hollywood stop, and walk East on Brookfield Ave. After it curves a little, turn right onto Burlington St, and then the next left onto Golf Rd. Walk straight on Golf Rd to the zoo. When you get to the zoo, there's a cut-through by the booths to walk into the parking lot.
From Chicago, the BNSF line leaves from Union Station. See the Metra website for more information about other stops and schedules. The easiest way to buy Metra tickets is using the Ventra app, or in person at Union Station. If you haven't used the Metra before, it's a commuter train so there may be quiet cars to look out for, and trains come roughly once an hour but sometimes less (or more, during rush hour times). Trains usually are roughly on time.
There are also busses that serve the area, but you'll usually need to make a couple of connections to get there. I'd recommend using Google Maps and clicking on the bus icon to get public transit suggestions.
TOPICS AND EXHIBITS