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Large configurational disorder in entropy-stabilized single-phase materials can lead to unique functional properties that deviate from traditional alloy mixing rules. Recently, it has been shown that entropy-stabilization can be applied to specific sublattices of transition metal oxide structures, adding to the already rich composition-structure-property phase space found in this class of materials. In particular, previous work on entropy-stabilized oxides (ESOs) has shown the formation of colossal dielectric constants, enhanced magnetic exchange couplings, and mixed phase magnetic structures. In this study, we have focused on the latter and combined bulk magnetometry and temperature-dependent neutron diffraction to better understand the magnetic structure formed in an ESO perovskite, with an emphasis on how long-range magnetic order forms despite large disorder of a cation sublattice. Specifically, we present here results on the A-site alloyed perovskite, (Y0.2La0.2Tb0.2Pr0.2Nd0.2)MnO3, or (5A)MnO3. Our magnetometry data show two sharp phase transitions as well as the presence of exchange bias at low temperature, suggesting a mixed phase magnetic ground state consistent with previous reports. Neutron powder diffraction shows clear long-range antiferromagnetic ordering below 60 K and Reitveld refinement of the diffraction data reveals that the two phase transitions can be attributed to ordering on the Mn and A-site sublattices, and that the dominant low-temperature magnetic ordering is Pn'ma'. Finally, we compare the remarkable similarities between the magnetic structure evolution in our (5A)MnO3 to NdMnO3 to highlight the insensitivity of magnetic structures to extreme disorder on the A-site of the perovskite lattice.