In this study, single crystals of FeIn2S4 and CuIn5S8 compounds, and (FeIn2S4)1−x(CuIn5S8)x solid solutions were grown using the Bridgman method. The magnetic and electrical properties of the samples obtained were investigated at temperatures of 5–300 K and in a magnetic field range of 0–14 T. It was established that all of the solid solutions were paramagnets down to low temperatures of ~10 K. It was shown that the ground state of the magnetic phase of the samples was a spin glass state, where the freezing temperature increased monotonically with the increase in the concentration of Fe2+ cations. All of the samples exhibited semiconductor characteristics in terms of electrical resistivity. The concentration-dependent critical magnetic temperatures, magnetic moment, and activation energy were plotted, which are probably explained by the magnetic state formation of the (FeIn2S4)1−x(CuIn5S8)x solid solution single crystals based on the empirical Goodenough–Kanamori rules.