The Middlegate Complex and Cabell’s Mill are near the meadow along Big Rocky Run and Walney Road. It is believed that the mill was built as early as 1769 but no later than the early 1800s. There are records indicating that there was another mill near Cabell’s Mill. That mill was built by Willoughby Newton around 1746. Middlegate served as the miller’s house and was probably built in the early 1800s. At various times, the mill was used as a grist, sumac and saw mill.
In 1944, Ellanor C. Lawrence purchased the Middlegate-Cabell’s Mill property. She and husband David, the founder and publisher of U.S. News & World Report, used it as a country retreat from the social and political influences of Washington, D.C. Middlegate served as the Lawrence’s residence when they visited the property. The mill was used to entertain guests and friends during various functions.
The Park Authority renovated Cabell’s Mill and Middlegate in 1979-80. The mill became a rental facility of the agency's Historic Properties Rental Services. Middlegate is used for park administration and maintenance offices and includes a caretaker’s apartment and a maintenance shop. Middlegate is closed to the public.