 Delacour's langur is endemic to Vietnam, where it is found only in an area around in the provinces of Ninh Bình, Hà Nam, Hòa Bình, Thanh Hóa, and Hà Tây in the north of the country.The largest surviving population is believed to be in Van Long Nature Reserve in Ninh Bình, where the monkey inhabits open forest up to elevations of , in terrain dominated by limestone karst.Delacour's langurs are diurnal, often spending the day sleeping in limestone caves, although they sleep on bare rocky surfaces if no caves are available.