The von Trapps inspired the classic 1959 stage musical and 1965 movie, "The Sound of Music," which is about how an aspiring nun helps seven children reconnect with their strict father and rediscover the joy of music after the death of their mother in pre-World War II Austria. The film starred Julie Andrews as the nun and Christopher Plummer as the father.
After the war, the real-life family moved to the United States and continued to perform. Younger members of the clan still tour.
Britain's Mirror newspaper said Agathe von Trapp died Tuesday after suffering heart failure last month.
She was the oldest daughter of Austrian naval officer Georg Ritter von Trapp.
The "Sound of Music" character Liesl, played by Charmian Carr in the film, was based on her.