Epitaxial thin films of ${\text{LaCoO}}_{3}$ $(e\text{-LCO})$ exhibit ferromagnetic order with a transition temperature ${T}_{C}=85\text{ }\text{K}$ while polycrystalline thin ${\text{LaCoO}}_{3}$ films $(p\text{-LCO})$ remain paramagnetic. The temperature-dependent spin-state structure for both $e\text{-LCO}$ and $p\text{-LCO}$ was studied by x-ray absorption spectroscopy at the $\text{Co}\text{ }{L}_{2,3}$ and $\text{O}\text{ }K$ edges. Considerable spectral redistributions over temperature are observed for $p\text{-LCO}$. The spectra for $e\text{-LCO}$, 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 $(S=0)$ state with decreasing temperature. This observation identifies an important prerequisite for ferromagnetism in $e\text{-LCO}$ thin films.