yes free so are the Art museums.. I still get a membership to the Zoo so parking is free and the Kids get to then go to special events.
We took the kids to the zoo this year. I paid for reserved parking through the parking panda app. That is the way to go. Got there and the lots were full showed them my app receipt and they opened the gate and told me to move any cone I'd like and park. Always been a big fan of the D.C. Zoo. Lots of shade and great exhibits