Thollon's red colobus lives in forests between rivers in the Democratic Republic of the Congo. The 2019 IUCN assessment reports that one studied group ate mostly leaves, along with seeds, fruit, and flowers.
Grubb's 2002 systematics draft describes no red color on the face and distinguishes its back's dark pattern and the tufts at the base of the tail from Bouvier's red colobus.
At one study site in Salonga National Park, the studied group ate mostly leaves, with seeds, ripe fruit, and flowers also recorded.
An extinction-risk assessment has not been added yet.