his work is a continuation of studies on the doping of chemically deposited PbS(I) layers and discusses the effect of cobalt ions on films’ morphological, structural, optical, and photoelectric properties. Elemental energy-dispersive analysis showed that cobalt was detected in films at the ≥0.04 mol/l CoCl2 concentration in the reaction mixture. The produced PbS(I, Co) films retain the B 1 cubic structure (space group). An established trend of the PbS(I, Co) films band gap increase from 0.57 to 0.75 eV is connected with an increase in the content of nanoparticles in them from 1 to ~8% for deposition during 1.5 h. For a 3-hour process, we also observed a bandgap increase from 0.57 to 0.68 eV corresponding to the fraction rise of nanoparticles - from 13 to ~28%. The concentration dependence of the PbS(I, Co) films volt sensitivity deposited for 1.5 h exhibits two maxima corresponding to 1 and 4% nanoparticle contents. During a three-hour synthesis process, a sharp photoresponse decrease was noted with an increase in the content of nanoscale particles to ~13-28% in the PbS(I, Co) layers. We showed that the photocurrent density decreases with an increase in the content of nanoparticles in the films in the series PbS(Co) →PbS →PbS(I, Co) →PbS