The crystal structures of the manganese oxide chlorides Sr2MnO3Cl and Sr4Mn3O8-yCl2 have been determined from neutron powder diffraction data collected at room temperature and at 2 K. The materials crystallize in the tetragonal space groups P4/nmm (Sr2MnO3Cl) and I4/mmm (Sr4Mn3O8-yCl2) and the structures are analogous to the n = 1 and n = 3 Ruddlesden−Popper phases Sr2MnO4 and Ca4Mn3O10. Both materials contain layers of highly distorted Mn(III)O5Cl octahedra. Sr4Mn3O8-yCl2, in addition, has a central layer of MnO6-δ octahedra with oxygen vacancies localized within the tetragonal plane. Consequently, the average coordination of the site is reduced to a mixture of 6-fold and 5-fold and some of the Mn atoms adopt pyramidal coordination. The level of oxygen deficiency within Sr4Mn3O8-yCl2 y = 0.44 confirms the Mn valence is predominantly +3. Magnetic susceptibility measurements indicate the onset of antiferromagnetic ordering (TAF) in the materials at 80 and 90 K for Sr2MnO3Cl and Sr4Mn3O8-yCl2, respectively. Antiferromagnetic order is confirmed by the presence of magnetic scattering in the low-temperature neutron diffraction data. The magnetic structure of Sr2MnO3Cl has been determined, yielding an ordered manganese moment μz = 3.74(5) μB at 2 K. In contrast, the magnetic scattering exhibited by Sr4Mn3O8-yCl2 suggests a level of magnetic frustration.