The Olive Colobus is confined to the forests of west Africa, and is discontinuously distributed from southern Sierra Leone and Guinea to south-east Nigeria. Oates' (1982) map shows a more or less continuous range from Sierra Leone to Ghana, extending just east of the Volta River, and again in Nigeria on the south bank of the Benue River just above its confluence with the Niger. He considered the distributional gap to be real rather than an artefact of collecting or observation (Groves 2001). In a few localities (e.g., Tai forest, Côte d'Ivoire), it is only locally distributed, but numerous. In a recent survey of Bénin and Togo, Campbell et al. (2008) found the Olive Colobus in 13 of the 26 localities surveyed in Bénin; no sightings were made in Togo by Campbell's team, although it was reported by hunters at one locality (see Campbell et al. 2008 for more details).