History comes alive at the 27th Annual Heritage Festival at McConnells Mill State Park. The Festival, sponsored by the Portersville-Prospect Rotary, celebrates the operational time period of the historical gristmill—from 1852 to 1928. The historic gristmill houses the fascinating machinery that ground the grain for the community surrounding Slippery Rock Gorge. Located in Kildoo picnic area, and the gristmill. Photo by Charlene Reinhart. Free admission and free parking!