The Putty-nosed Monkey is an arboreal species present in lowland and mid-elevation montane tropical moist forest, gallery forest and secondary forest; it is less commonly found in swamp forest. This species generally lives in groups of between 12 and 30 animals. It prefers the middle and upper strata of the forest canopy, and is uncommonly encountered below 10 m or on the ground (Gautier-Hion 2013).

Cercopithecus nictitans occurs as a disjunct population in Liberia and western Côte d'Ivoire, and then more continuously from the Osse River in western Nigeria south and east to the Congo River, across the Ubangui River as far east as Buta and Budjala (both in Democratic Republic of Congo) between the Congo River and Ubangui River. It is also found on the island of Bioko (Equatorial Guinea). Isolated of western population is thought to have resulted from competition with Cercopithecus diana.

There are five subspecies: insolitus, ludio, martini, nictitans and stampflii.

Cercopithecus n. insolitus is found in central-southern Nigeria, from the Niger Delta in the south to north of the Niger and Benue rivers. Its range extends westwards within much of the extent of the Nigerian lowland rainforest ecoregion.

Cercopithecus n. ludio occurs in southeastern Nigeria and southwestern Cameroon in the area between the Cross and Sanaga rivers, as far as the Mbam River, east of which it is replaced by C. n. nictitans. Almost half their range lies north of the Cross River to the Mambila Plateau and the forested areas of Gashaka Gumti National Park in Nigeria, and corresponding areas in Cameroon, including Takamanda National Park.

Cercopithecus n. martini is restricted to Bioko Island, Equatorial Guinea, where its range is limited to approximately 280 km² in one protected area in the south—the Gran Caldera Scientific Reserve.

Cercopithecus n. nictitans—is generally distributed through the moist forests south of the Sanaga river east to the Itimbiri River and down into the northern Congo Basin, along the right bank of the Congo River to the forest-savanna limits. Its range encompasses mainland Equatorial Guinea, Gabon and parts of Cameroon, Central African Republic, Democratic Republic of Congo and Republic of Congo. It may also be present in Angola (Cabinda). The Sanaga river is not a hard northern barrier; however, as in its northwestern extent, its range crosses the Sanaga River, extending northward east of the Mbam River into the Cameroon Highlands [where it meets the eastern limit of C. n. ludio in the vicinity of the Mambilla Plateau along the Nigeria-Cameroon Border] (Grubb et al. 2000, Oates 2011).

Cercopithecus n. stampflii occurs in the disjunct western part of its range, distributed across northern Liberia and western Côte d’Ivoire. In Côte d’Ivoire, it is believed extirpated from nearly all its former range, except for Taï National Park. The current distribution of C. n. stampflii in Liberia is unknown; one specimen was recently recorded by Covey and McGraw (2014) in a bushmeat market along the Liberia-Côte d’Ivoire border, but it was not encountered by Abdulai et al. (2007) in a rapid survey of North Lorma, Gola and Grebo National Forests of western Liberia.

Cercopithecus nictitans is listed on Appendix II of CITES and on Class B of the African Convention on the Conservation of Nature and Natural Resources. It is on the list of partially protected species in Nigeria, Congo and DRC, and on Class C in Cameroon and CAR (i.e., may be hunted with a permit). The hunting, sale or consumption of primates is forbidden in Equatorial Guinea by Presidential Decree. All primates are fully protected in Cross River State, Nigeria, under the Forestry Commission Law of 2010. It is not listed as a protected species in the legislation of either Gabon or Côte d'Ivoire.

This species occurs in almost all the protected areas in its range, including the World Heritage sites of Dja (Cameroon), Lope (Gabon) and the Sangha Trinational (Congo-Cameroon-CAR). In southeastern Nigeria, the species is present in Afi Mountain Wildlife Sanctuary, Cross River National Park and Mbe Mountains (all in Cross River State), and in Gashaka Gumti National Park in Taraba State. Due to its rarity, the western-most form, C. n. stampflii, occurs in very few protected areas; Taï National Park (Côte d'Ivoire) is a notable exception.