Count Otto of Duras (d. 1147) was a count of Duras, and advocatus of the nearby abbey of St Truiden. Duras and St Truiden are in the modern province of Belgian Limburg. His parents were Count Giselbert of Duras and his wife Gertrud.
Otto married Berthe of Valenciennes, daughter of Yolande of Guelders, daughter of Gerard I, Count of Guelders. Yolande was first married to Baldwin III, Count of Hainaut, and was mother to Baldwin IV, Count of Hainaut.
Otto and Berthe are thought to have had one child who survived to adulthood, Otto's successor:
In Sint-Truiden charter 51 (Piot Vol.2) Countess Juliane was described as Otto's filia, and her Juliane's husband Count Godfried was described as his gener. This could mean "son-in-law" or "brother-in-law". (In the 19th century Wolters for example identified Juliane as Otto's sister, but this seems unlikely given the succession of the Counts of Duras.)
Juliane and Godfried had five children, the eldest of which was Gilles, Count of Montaigu, Duras, and Clermont, who married Lauretta, daughter of Louis I, Count of Loon. Their third son Conan was also Count of Duras. None of Juliane's sons had male heirs, and the family inheritance split up after their deaths.