The synthesis of Sr2FeO3 through a hydride reduction of the Ruddlesden-Popper layered perovsldte Sr2FeO4 is reported. Rietveld refinements using synchrotron and neutron powder diffraction data revealed that the structure contains corner-shared FeO4 square-planar chains running along the [010] axis, being isostnictural with Sr2CuO3 (Immm space group). Fairly strong Fe-O-Fe and Fe-Fe interactions along [010] and [100], respectively, make it an S = 2 quasi two-dimensional (2D) rectangular lattice antiferromagnet. This compound represents the end-member (n = 1) of the serial system Srn+1FenO2n+1, together with previously reported Sr3Fe2O5 (n = 2) and SrFeO2 (n = infinity), thus giving an opportunity to study the 2D-to-3D dimensional crossover. Neutron diffraction and Mossbauer spectroscopy show the occurrence of G-type antiferromagnetic order below 179 K, which is, because of dimensional reduction, significantly lower than those of the other members, 296 K in Sr3Fe2O5 and 468 K in SrFeO2. However, the temperature dependence of magnetic moment shows a universal behavior.