The park covers an area of 560 acres (2.3 km2)[1] along the eastern shore of the Black River and is located between Long Valley and Chester.

Its land represents a glacial valley carved by the Black River and some of its tributaries.

The park is home to the Nathan Cooper Gristmill, the Elizabeth D. Kay Environmental Center, the Bamboo Brook Outdoor Education Center, and the Willowwood Arboretum.

When Alfred and Elizabeth Kay moved from Pittsburgh to the area in 1924 they consolidated land to establish the Hidden River Farm; later some of their land was donated to the park system.

The park is used for hiking, fishing, bird watching as well as for activities through its educational centers.