A road along the present path of SR 120 has existed at least since the 1750s. This road, linking Alexandria to Great Falls, was first known as the "Road to the Falls." It took its present name from the nearby glebe lands that were used to support the clergy of the colonial Fairfax Parish of the Church of England; those lands also gave their name to the historic Glebe House, which was built in the 19th century on the former glebe property and sits near what is now SR 120.