In 1324, a Willem van Bronckhorst sells a good in "Hacvorde" to Jacob van der Welle, who then went on to call himself Van Hackfort. Leenheer remained the Van Bronckhorsten until 1702. In 1581, it came into the Van Raesfelt family's possession via their heiress daughter Jacoba van Hackfort. In 1602, through their daughter Margarethe, the succession to her cousin Borchard van Westerholt, who had rebuilt the castle before her death. It remained in the possession of the barons Van Westerholt for centuries.
When Borchard Frederik Willem, the second-generation from the Westerholt family, died in 1934, he left his five children as heirs. They were all unmarried except for Clara. Clara was huddled in 1935. Her brother and three sisters remained owners for a quarter each. In 1964 'freule sister' died from The Hague. She gave her quarter to Natuurmonumenten. In the same year her brother Arend made a will in which he also left his quarter to Natuurmonumenten. Arend and his sisters continued to manage until the last heir died. Arend died on October 8, 1970, his sister freule Emma on November 28, 1971. Sister Sannie was then the only person in charge of Hackfort. Freule Sannie was the last Westerholt to die on April 14, 1981
