A detailed survey of Hoolock hoolock was carried out in the Inner-Line Reserve Forest and the adjoining areas of Cachar district of southern Assam, India, from July 2010 to December 2011. About 150 km2 of the area was covered. In direct sighting, groups and individuals were counted in 7 localities (39.7 km2). Only 3.96 km2 of the actual forest area were occupied by these gibbons. Nine family groups and a solitary subadult, 33 individuals in all, made up the total count. Of these, adult males and females comprised 54.5% of the population while the subadults, juveniles and infants comprised 27.3, 12.1 and 6.1%, respectively. Each family group's home range was 0.31-0.51 km2. Of the 7 localities, only 1 had more than 1 family group. Habitat destruction and diverse threats to the hoolock gibbon in this area are examined in this paper.