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.

Few more changes were made at Idlewild Park until February 1983 when Kennywood Park Corporation took ownership.

The future of Idlewild is one of growth and improvement. Yet despite this progress, the Park will always maintain the natural beauty and romantic atmosphere that attracted families over a century ago