In 1940, after a succession of owners, the property was purchased by Mr. and Mrs. James H. Symington. The Symingtons set about restoring the house and making improvements to the farm.
The Symingtons succeed in restoring the mansion house, making extensive renovations and modernizing the home by adding indoor plumbing and electricity. They planted a variety of crops, eventually specializing in popcorn and becomeing for a time one of the largest suppliers in the eastern United States. When the popcorn market collapsed after World War II, however, they turned increasingly to raising livestock, including cattle and hogs, as well as wheat, corn and hay for animal feed. Mrs. Symington took over the management of the day-to-day farm operations after her husband became ill in the 1970s, and continued to run it after his death. Concerned about th e rapid development that was beginning to spread into Loudoun County. Mrs. Symington donated the 286-acre farm to the Northern Virginia Regional Park Authority (NVRPA) in 1985. Since that time, the NVRPA has operated Temple Hall as a working farm and interpretive center, educating visitors about farm life while preserving the farm as a rural, agricultural landscape.