In 1809, the sister of Henry Lee III - the Revolutionary War hero known as "Light Horse Harry," and the father of Robert E. Lee - bought the place.
That lineage has attracted interest for decades. Greenhalgh remembers her parents and aunts, who lived in different wings of the house, giving impromptu tours to visitors and scholars who would show up unannounced. Plaques by the front door honor the house's place on the National Register of Historic Places and Virginia's list of historic landmarks.
Architects have drawn a link between Fairfield and Kenmore, the home of George Washington's sister Betty, near Fredericksburg. The central layouts of the two houses are identical, and both may have been designed by noted colonial architect John Arlis. Arlis, in fact, asked to be buried at Fairfield, and Greenhalgh remembers her father showing her a clutch of ancient graves, now lost.
"It is a very good Georgian house," said Ed Chappell, director of architectural research at Colonial Williamsburg, who wrote a study of Fairfield in 2009. "In addition to its sort of blue-ribbon history, it is one of the late colonial Virginia houses that survived in very good shape."
Many grand old houses didn't survive a rash of remodeling in the early 20th century that turned historic properties into modern estates, Chappell said. He cited James Madison's Montpelier, which just completed a $25 million restoration to its original state.
George Greenhalgh pulled out a sheaf of yellowed blueprints to show what could have gone awry at Fairfield - a series of proposed changes through the decades, from massive colonnades to high Victorian domes.
"We dodged a bullet," George said.
"Thank goodness," Robin said.
The house, often studied, continues to reveal surprises. In an old magazine article about Fairfield, Greenhalgh was astonished to find a reference to a "master's retreat" and a fuzzy photograph of a huge room with a vaulted wood ceiling. A mighty elk head loomed over the fireplace. News to the family. It turned out the "retreat" was an early iteration of their own living room; they found the wood paneling, intact, above their ceiling. Future owners may want to restore that room, she said.
Two and a half centuries of private control have kept Fairfield intact, Boyce said. He and other historians hope the next owner will keep up the tradition.
Boyce knows firsthand the constant challenge of running a farm that predates the steam engine. "I have a staff and an endowment, and it's still daunting," he said. "One hopes that the buyers of Fairfield will know what they are getting into and have an appreciation for it. You're buying a way of life. It's going to take someone special."