Hardenbergh died on 30 October 1790 of tuberculosis in New Brunswick, New Jersey. He was interred in the churchyard of the First Reformed Church in New Brunswick. The inscription on his grave was written by the Reverend John Henry Livingston and exhorts mourners to "go walk in his virtuous footsteps; and when you have finished the work assigned you, you shall rest with him in eternal peace." It eulogises Hardenbergh as "a zealous preacher of the Gospel, and his life and conversation afforded, from his earliest days, to all who knew him, a bright example of real piety...a steady patriot, and in his public and private conduct he manifested himself to be the enemy of tyranny and oppression, the lover of freedom, and the friend of his country." At the time of his death, Hardenbergh was a wealthy man—largely due to monies and property inherited from his father and grandfather—and was the owner of 40,000 acres of land in Ulster County that was once part of his grandfather's patent.