Born Dorothy Powell Ridgely in Baltimore, she was the daughter of D. Stewart Ridgely and the former Dorothy Powell. Her father was in the last generation of his family to be born at Hampton, the Baltimore County landmark.
Mrs. Thomas was a descendant of Charles Carnan Ridgely, Maryland's governor from 1816 to 1819.
She grew up in a family residence, Fallowfields, in Lutherville and attended the Calvert School. She was a 1948 Bryn Mawr School graduate and earned a bachelor's degree from Vassar College. She made her debut at the Bachelors Cotillon in 1949.
She taught hearing-impaired students at the William S. Baer School for several years before leaving to raise her family.
"My mother was a believer in keeping traditions and in taking care of her family," said a daughter, Catherine Stewart Thomas Burnett of Baltimore.
Family members said Mrs. Thomas was active at the Hampton mansion and volunteered for many years. She helped decorate it at Christmas and helped staff its gift shop. She belonged to the Women's Committee of Hampton National Historic Site and Historic Hampton Inc.
She was a member of the Amateurs Garden Club and volunteered in the Church of the Holy Comforter's altar guild. She was also a Bryn Mawr School and Elkridge Club dancing class volunteer.
She belonged to a reading club called the Book Worms, played tennis and attended performances at the Baltimore Symphony Orchestra and the old Mechanic Theatre. She also raised English cocker spaniels.
Services will be held at 2 p.m. Wednesday at St. Thomas' Church, 232 St. Thomas Lane in Owings Mills.
In addition to her daughter, survivors include her husband of 56 years, Andrew Banks Thomas Sr., a retired banker; a son, Andrew Banks Thomas Jr. of Charlotte, N.C.; another daughter, Dorothy Thomas Eckhardt of Cumberland Center, Maine; a brother, David Stewart Ridgely Jr. of Cambridge; 12 grandchildren; and two great-grandchildren. A daughter, Emily Thomas Wiley, died in 2009.