Chilko River adopted 26 June 1911, not "Chilco River" as spelled on Trutch's 1871 map of BC, nor "Chilcote River" another variation.
Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office
"From a Chilcotin ... word meaning 'ochre river' ...[Chilcotin] can be translated as 'ochre river people' here referring not to the colour but to the mineralized substance (usually red or yellow) much prized by the [First Nations] for use as a base for paint or dye."
Source: Akrigg, Helen B. and Akrigg, G.P.V; British Columbia Place Names; Sono Nis Press, Victoria 1986 /or University of British Columbia Press 1997