Strained thin films of SrTiO3 perovskite possess a paraelectric to ferroelectric (FE) phase transition which is suppressed in bulk SrTiO3 due to quantum fluctuations. Although the stabilization of ferroelectric SrTiO3 has a significant technological relevance, it is still poorly explored. With this proposal we aim to study two aspects of the FE transition in SrTiO3: the formation and evolution of ferroelectric domains (if any), and the understanding of the competition between the FE transition and a ferroelastic antiferrodistortive (AFD) transition which occurs independently in SrTiO3. To do that, we propose to perform a cryogenic diffraction experiment at BM02 for SrTiO3 thin films grown under a range of biaxial strain, spanning from compressive (grown on NdGaO3 substrates) to tensile (grown on DyScO3 substrates), which will help us unravel the associated structural modifications and domains formation in SrTiO3 thin films.