National Park Service
Leashed pets are welcome on all park trails, parking lots, falls overlooks, and picnic areas. There are no off-leash areas in Great Falls Park. Owners must have physical control of the animal, using a six foot leash, at all times. Electronic or 'shock' collars do not count as a leash. With the exception of service dogs, pets are not permitted in the visitor center, or on ranger-led programs.
An off leash dog park is available in Reston, about fifteen minutes from Great Falls Park. Other off leash parks are located in Herndon, Arlington, Alexandria city, and Vienna.
During the warmer months, remember not to leave your pet unattended in a car. Temperatures in closed vehicles can be fatal to pets.