Idlewild Park came into existence when William Darlington, owner of the property, gave "the right and privilege to occupy his land for picnic purposes or pleasure grounds" to Judge Thomas Mellon, owner of the Ligonier Valley Railroad. The date was May 1, 1878. The Park continued its success as a picnic area, enticing city dwellers for a weekend in the country aboard the Ligonier Valley Railroad, which had a station at the Park.

1952 saw the end of the Ligonier Valley Railroad. Under the new owners, the Macdonald Family, who purchased the Park from the Mellons in 1951, Idlewild Park continued to grow and improve. Story Book Forest was added in 1956.