Indium sulfide thin films were successfully deposited on soda lime glass substrates by modulated flux deposition (MFD) at significantly lower substrate temperatures than in previous experiments. The influence of both experimental parameters sulfur source temperature (TS) and substrate temperature (T) on the optical, structural, and chemical properties were studied. Amorphous indium sulfide layers were obtained at T = 100 °C and crystallized as β-In2S3 for T ≥ 150 °C. Quite high values were required for the TS parameter in order to ensure the formation of transparent β-In2S3 thin films. No other polycrystalline phases were detected. Direct optical bandgaps of 2.58 eV (amorphous In2S3) and 2.73 eV (β-In2S3) were estimated for film thicknesses of around 100 nm.