Owing to the strong connection between strain and ferroelectricity, large shifts of the Curie temperature and polarization are observed in strained ferroelectric material. In this work, the effects of lattice-mismatch induced stress upon the crystallographic structure, strain, and generation of different types of defects in epitaxial SrTiO3 films on CeO2 buffered sapphire are examined and discussed in context with the resulting impact of strain on the polarization of the ferroelectric layers. Depending on the thickness of the SrTiO3 layer, characteristic changes in their structural perfection and crystallographic orientation with respect to the substrate system are observed. For thin films, misfit dislocations partially compensate the stress in the SrTiO3 layer, whereas cracks develop in thicker SrTiO3 films. The structural modifications and the formation of defects are explained in a model based on lattice misfit induced stress and energy considerations. It is demonstrated that intrinsic mismatch and thermal mismatch must be considered to explain strain dependent effects such as induced ferroelectricity and modifications of the permittivity of these complex heteroepitaxial layer systems.