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Epitaxial thin films of LaCoO 3 ͑e-LCO͒ exhibit ferromagnetic order with a transition temperature T C = 85 K while polycrystalline thin LaCoO 3 films ͑p-LCO͒ remain paramagnetic. The temperature-dependent spin-state structure for both e-LCO and p-LCO was studied by x-ray absorption spectroscopy at the Co L 2,3 and O K edges. Considerable spectral redistributions over temperature are observed for p-LCO. The spectra for e-LCO, on the other hand, do not show any significant changes for temperatures between 30 and 450 K at both edges, indicating that the spin state remains constant and that the epitaxial strain inhibits any population of the low-spin ͑S =0͒ state with decreasing temperature. This observation identifies an important prerequisite for ferromagnetism in e-LCO thin films.