She was 93.
"She was quite a lady and the great steward of Wye House. It is a seven-part Georgian-period house that was built in 1782 and is an extraordinary one," said Walter G. Schamu, a partner in the firm of Schamu, Machowski, Grego Architects, who designed several projects at the house.
"She was always very friendly and cordial. Even though I found her somewhat formal, she was a very warm and genuine person who had the history of the house at her fingertips," said Mr. Schamu.
Mary Donnell Singer was born in Pittsburgh. After her parents divorced, she lived with her paternal grandmother there during the school year and on the Eastern Shore during summers.
Mrs. Tilghman, who was known as "Mimi" to family and friends, graduated from the Ellis School in Pittsburgh. After earning a bachelor's degree from George Washington University, she moved back to the Eastern Shore and lived with her mother near Easton.
She met her future husband, Dr. R. Carmichael Tilghman, in 1938 at a family Christmas party at Gross Coate Farm in Talbot County.
During World War II, Mrs. Tilghman was a plane spotter in Tunis Mills. She wed Dr. Tilghman, a Johns Hopkins internist, in April 1945 after he returned from serving with the 18th General Hospital, one of two Hopkins units in the South Pacific.
The couple lived for many years in the Four Winds neighborhood of Ruxton, where they raised their four children.
In 1993, after inheriting Wye House from her great-aunt, Elizabeth Lloyd Schiller, Mrs. Tilghman and her husband moved into the house, which overlooks the Wye River and is surrounded by 147 acres.
"My own aunt, Elizabeth Lloyd Schiller, who lived here for so long, used to tell me, 'You don't own Wye, it owns you,' " Mrs. Tilghman told a Baltimore Sun reporter in a 1999 interview.
Mrs. Tilghman was a direct descendant of Edward Lloyd, a Welsh Puritan and an early tobacco planter who came to Maryland in the early 1650s and acquired the Wye House property in 1659. Frederick Douglass, who became an outspoken anti-slavery advocate, author and statesman, had lived at Wye House as a slave in his boyhood.
Beginning in 1993, Mrs. Tilghman embarked on an effort to preserve not only Wye House but its surrounding gardens and outbuildings.
She also actively promoted research on the history of the Lloyd family and Wye House and commissioned the Maryland Historical Society to catalog the many Lloyd and Tilghman family papers so they would be more readily accessible to historians and scholars interested in the study of Maryland's Tidewater Barony era and plantation life.
She also opened the home, which is a National Historic Landmark, to numerous groups for tours, many of which she personally led until she was in her 90s.
Mrs. Tilghman made Wye available to Preservation Maryland, Eastern Shore Land Conservancy and the Historical Trust of Talbot County for fundraising events.
Beginning in 2005, Mrs. Tilghman invited archaeologists from the University of Maryland, College Park to conduct digs on the property, which they have done for the past seven summers.
However, the current Wye House is not the original.
"In 1781, the original house burned, leaving only a small part of it, an outbuilding, the Captain's House, that is still standing," said Mr. Schamu. "And its orangery, which dates to the 18th century, is still in use."
According to the National Trust for Historic Preservation, the Wye House orangery is believed to be the only surviving 18th-century greenhouse extant in North America, where oranges, lemons, roses and medicinal herbs were grown.