Little is known about the genealogy and the biography of Eleonora Ziemięcka née Gagatkiewicz. Poland’s first female philosopher (1819–1869). This article, the fruit of extensive archival research, now supplies the missing data. It not only fi xes her birth date – hitherto unknown – but also gives us an insight into the circumstances and reasons of her being brought up away from her parents. It has also been possible to collect a good deal of information about her relations, especially the Gagatkiewicz family (she was the granddaughter of Walenty Gagatkiewicz, the most distinguished physician of late 18th century Warsaw), and the family connections and the profi le of her husband, the portrait painter Antoni Ziemięcki.