We have studied the crystal structures of (Sr₀.₈Ce₀.₂)(Mn₁_yCoy)O₃ (y = 0 and 0.2) using neutron diffraction. Both (Sr₀.₈Ce₀.₂)MnO₃ and (Sr₀.₈Ce₀.₂)(Mn₀.₈Co₀.₂)O₃ have a tetragonal structure in space group I4/mcm at room temperature, and the octahedral tilt angle around the c-axis is nearly the same. The only significant difference is the shape of the Mn(Co)O₆ octahedron: it is elongated in (Sr₀.₈Ce₀.₂)MnO₃ due to the cooperative Jahn–Teller (JT) effect, but essentially regular in (Sr₀.₈Ce₀.₂)(Mn₀.₈Co₀.₂)O₃ due to the absence of JT-active Mn³⁺ ions. With increasing temperature, both compounds undergo a continuous phase transition at around 400°C to a cubic structure in Pm3m, with no indication of a distinct transition in (Sr₀.₈Ce₀.₂)MnO₃ from the removal of the static JT distortion. In addition, the temperature dependence of the octahedral tilt angle is very similar in the two samples, implying that the JT distortion has minimal effect on the octahedral tilting and the phase transition to cubic. X-ray absorption near-edge structure (XANES) analysis indicates that the Ce oxidation state is predominantly 4+ in both samples. The electrical conductivity is higher in (Sr₀.₈Ce₀.₂)MnO₃ than in (Sr₀.₈Ce₀.₂)(Mn₀.₈Co₀.₂)O₃ in the temperature range studied (100–900°C).