Pb1+хS thin films of 190–360 nm thickness have been synthesized on glass substrates by chemical bath deposition from aqueous solutions using different thioamides (thiourea, N-allylthiourea, thioacetamide) as sulfur precursors. The obtained films are polycrystalline semiconductors with n-type conductivity. The effect of the sulfur origin on the crystalline structure, morphology and formation mechanism of Pb1+хS thin films is analyzed. The formal rate constants of Pb1+хS formation reactions are determined. Quantum-chemical calculations approve that a lead superstoichiometry in the obtained films may be attributed to types of point defects: atomic vacancies in the sulfur sublattice and the lead doping the sulfur sublattice. A correlation is established between the amount of lead excess and the optical band gap of Pb1+хS: the greater the excess of lead is, the wider the band gap is. The fractal analysis of Pb1+хS thin films evidences the film growth obeying model of a cluster-by-cluster association in three-dimensional space.