In the present work, we have studied the effect of a post-annealing process on the magnetic properties of thin films of Cr-doped indium oxide, In2−xCrxO3−δ. Samples with low stoichiometric oxygen deficiency, δ, which is required for ferromagnetic behavior, were fabricated using a DC/RF magnetron sputtering method. The post-annealing process described in this paper allows control of the oxygen deficiency. This method has led to samples which show clear ferromagnetic behavior at both low temperatures and at room temperature with saturation magnetic moments up to ∼1.5 µB/Cr-atoms. The measured high Curie temperature, TC ∼ 740 K, justifies the indirect electron-mediated ferromagnetic coupling of the spins of Cr ions. The ferromagnetic coupling was found to be mostly a bulk effect, which is not affected by the surface of the film.