Mariposa Park just outside Newton is a Jasper County Park. The park has a 1 mile loop trail around the lake, a small playground with a fire pit and picnic shelter nearby, and a large nature playscape. After entering the park, you'll pass one parking area before coming to the one closest to the playground.
If you see a picnic shelter, you're in the right spot. There's a vault restroom next to the parking area. From there, head down the hill and turn right for the nature playscape, go straight for the hiking trail and head left for the playground. Don't forget a painted rock to extend the length of the rock snake.