The Heishan Nature Reserve in Wansheng Economic and Technological Development Zone of Chongqing is a crucial habitat for the endangered Trachypithecus francoisi in Chongqing, China. To assess the current population status and distribution of this species within and adjacent to the reserve, field surveys were conducted from April to December 2022 and from August to December 2024. The methodologies include direct observation counting, infrared camera trapping, and non-induced interviews with local communities. Results demonstrate that T. francoisi population was primarily confined to both sides of the Liyu River valley, encompassing an area of approximately 20 km2. The population size increased from 63 individuals in 2022 to 66 in 2024, corresponding to a growth rate of 4.76%. By 2024, nine groups and one solitary individual were recorded. Group sizes ranged from 3 to 13 individuals, with an average size of 7.2±2.7. The overall population density across the entire reserve and its adjacent area was 0.70 individuals·km-2, whereas the ecological density within the core distribution area was 3.3 individuals·km-2. Age structure analysis indicates that juveniles, subadults, and adults accounted for 13.64%, 21.21%, and 65.15% of the population, respectively. Notably, 86.36% of the individuals inhabited areas inside the reserve boundaries, with the remaining 13.64% located outside. These findings provide a scientific basis for the conservation of T. francoisi and their habitat in this region.