According to John Howard Raven and William H.S. Demarest, Hardenbergh obtained an education from the Kingston Academy, in Kingston, Ulster County, New York. However, the Kingston Academy was not established until 1773. Kingston did, however, have a small school with a Dutch schoolmaster founded in 1722 by the Trustees of the Freeholders and Commonality of the Town of Kingston—an organization chartered by colonial governor Thomas Dongan to provide for the free education of Kingston's children. In his late teens, he travelled to Somerset County, New Jersey to receive religious and theological instruction from the Reverend John Frelinghuysen, who was serving Dutch Reformed congregations in the Raritan valley of central New Jersey.