Great Falls Park is closed at dark.  Overnight camping is prohibited and there are no lodging facilities within the park. 

There are many options for lodging within the immediate area. A web search will provide a variety of choices.  Nearby towns include Reston, Herndon, Tysons Corner, Falls Church, Arlington, Alexandria, Sterling, and Washington D.C.

Nearby Camping:

Fairfax County Park Authority

Northern Virginia Regional Park Authority

Chesapeake and Ohio Canal NHP

Prince William Forest National Park

Shenandoah National Park

Catoctin Mountain National Park

Greenbelt National Park