Daniel Kennedy constructed the first gristmill along Slippery Rock Creek in 1852. Several years later it was destroyed by a fire and rebuilt in 1868. In 1875 Captain Thomas McConnell purchased the mill and replaced the water wheel and grinding stones with more modern water turbines and rolling mills.
According to the DCNR website, it processed corn, oats, wheat and buckwheat for local customers. Eventually it closed in 1928.
When Captain Thomas McConnell died, the mill was passed to his son James McConnell. Since James had no children at the time of his death years later, the property was given to the grandson of Captain McConnell, Thomas H. Hartman. Wishing the area to be preserved for future generations, Thomas H. Hartman transferred ownership of the mill and land to the Western Pennsylvania Conservancy in either 1942 or 1946.
McConnells Mill State Park was formally dedicated in October of 1957
and in May 1974 the U.S. Department of the Interior designated it a
National Natural Landmark.
Currently the park covers around 2546 acres and is considered one of the "Twenty Must-See Pennsylvania State Parks." The land is also designated as an Audubon Important Bird Area for its outstanding value to bird conservation.
Source and More Info:
Pennsylvania Department of Conservation and Natural Resources,
Great Natural Areas in Western Pennsylvania,
National Registry of Natural Landmarks (PDF),
Slippery Rock University - Online Rocket,
26 minutes ago