In this study, various techniques, such as energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, and spectrophotometry, were used to analyze the properties of nanometric CdS particles synthesized with varying precursor concentrations. EDX analysis revealed the nonstoichiometric composition manifested by an increase in the Cd/S ratio from 1.02 up to 1.43 with increasing precursor concentration. The growth of lattice parameters and unit cell volume accompanying preferential crystallization of the hexagonal phase along with an increasing Cd/S ratio was confirmed by XRD analysis. This indicated the presence of interstitial cadmium in nonstoichiometric Cd1+xS. The formation of shallow Cdi donor levels below the bottom edge of the conduction band impacts the bang-gap energy; a decrease from 2.56 to 2.21 eV along with increasing nonstoichiometry was observed. This is accompanied by a widening of the range of absorption of light, which creates conditions that can lead to an increase in the efficiency of redox reactions in photochemical processes.