Tunable spin polarizations up to 85% have been reported in bulk Co1-x Fex S2. In this paper, we report on the synthesis of polycrystalline Co1-x Fex S2 thin films on Al2O3 (0001) and SrTiO3 (001) by ex situ sulfidation of epitaxial Co1-x Fex. As a function of sulfidation temperature (TS), the films evolve from unreacted Co1-x Fex, through a mixed phase dominated by Co1-xFexS, to single-phase Co 1-xFexS2 at TS 350 °C. At optimized deposition conditions, the films are sulfur stoichiometric, have an average in-plane grain size of 35 nm, surface roughness of 3.7 nm (at a thickness of 56 nm), and are delamination-free up to 300 nm. The Curie temperature, saturation magnetization, resistivity, and magnetoresistance are similar to those of bulk. Significantly, we find 1.0 μB /Co at x=0.15 and a vanishing spin-flip electron-magnon scattering signature in magnetotransport, consistent with the very highly polarized state observed in bulk crystals. Ex situ sulfidation is therefore a simple route to the formation of Co1-x Fex S2 films, opening up the possibility of exploiting this unique material in fundamental studies of heterostructured spintronic devices.