In Malaysia, Sarawak it is estimated that less than 1,000 animals live in patchily distributed populations. In Sabah, the few substantial populations live within the Kinabatangan flood plain, and around Dewurst Bay (Eastern Deltas).
Only one population can be found in Brunei.
However, the species holds greater numbers in Kalimantan (Indonesian Borneo) These Indonesian populations differing in size ranges from 100-1000 depending on past and current threats (Meijaard and Nijman 2000).
Habitat
The Proboscis Monkeys are generally found in riparian-riverine forests, coastal lowland forest, which also includes mangroves, peat swamps, and freshwater swamp forest (Boonratana 2000). Always seen located near its local habitat’s waterway (Meijaard and Nijman 2000).
Why these areas?
It has been deduced that it is restricted to the coastal areas or sites near rivers largely due to the fact that these areas contain soils that are high in minerals and salts, a necessary part of its diet (Bennett and Sebastian 1988). They also tend to prefer low elevations, up to no more than about 350 m above sea level (Meijaard and Nijman 2000).