The park was across Shirland Avenue from Shrefler's Greenhouse which was on the south side of the street. Shirland Avenue is the Wisconsin/Illinois border so the park was in Beloit, Wisconsin versus South Beloit, Illinois.
The following is taken from a short history of the Larson/Ramquist and Hill families written by Carl Harold Ramquist II in 1983 at age 75 who was living in Beloit at the time of his death.
An amusement park, Interstate Gardens, was opened on the corner of Shirland and Moore. It had a roller coaster, shooting gallery, and various amusements, an outdoor dance pavilion, open Saturday and Sunday nites. Street cars came up Grand Avenue, went south on Moore street to the park, then north on Moore to Liberty and back to town.