The focal point of the park is a 137-acre lake that was developed by impounding Hills Creek. The earth dam, built by the Commonwealth of Pennsylvania, is 34 feet high and 422 feet long. The basin of Hills Creek Dam is long and narrow ending in an irregular triangle at the north end. The elevation is 1,486 feet and the nearby mountains rise to an elevation of 2,200 feet. The general area now covered by water has been almost continually, since the end of the last ice age, under the influence of beaver dams and beavers.
Beavers still abound in the locality, including Hills Creek Lake.
The temperatures and chemical characterizations of the lake support a good warm water fishery. Wildlife abounds in and around Hills Creek State Park. Along with the active beaver colonies are other water loving creatures like muskrat, wood duck, Canada goose and osprey. Wild turkey, deer, black bear, rabbit, grouse, pileated woodpecker, and woodchuck are also quite numerous in the surrounding mountains and field areas. The land was originally known as Kelly's Swamp when it was purchased in 1950.