Zn1-x Fe (x) S (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.12, and 0.15) samples have been synthesized by the chemical co-precipitation method, using ZnCl2 and Na2S as starting materials, FeCl3 as a dopant and Ethylenediaminetetraacetic acid (EDTA) as capping agent. Investigations of the structural, optical, and magnetic properties of the prepared samples have been carried out. The results of X-ray diffraction (XRD), selected area electron diffraction of TEM images, Fourier transform infrared spectroscopy have shown that Fe ions are incorporated into the lattice of ZnS crystallites as substitutional impurity at Zn sites in the structure without disturbing the original ZnS wurtzite structure. The average crystallite size from the XRD data and transmission electron microscopy has been found to be in the range of 4-10 nm. Magnetization behavior (i.e., M-H Characteristics) shows the evolution of ferromagnetic behavior with Fe incorporation. It has been found that there is an optimum iron ion concentration for observing the maximum magnetization. The optimum iron ion concentration has been found to be, x = 0.08 in the synthesized samples of Zn1-x Fe (x) S. The observed magnetization behavior has been understood as ferromagnetic behavior of Fe ions. The decrease of ferromagnetism for the higher Fe ion concentration has been discussed as a result of Fe-Fe interaction in close proximity to result antiferromagnetism for decreasing the magnetization.