Photosystem II (PSII) of photosynthetic organisms converts light energy into chemical energy by oxidizing water to dioxygen at the Mn4CaO5 oxygen-evolving complex (OEC). Extensive structural data have been collected on the resting dark state (nominally S-1 in the standard Kok nomenclature) from crystal diffraction and EXAFS studies but the protonation and Mn oxidation states are still uncertain. A "high-oxidation" model assigns the S-1 state to have the formal Mn oxidation level of (III, IV, IV, III), whereas the "low-oxidation" model posits two additional electrons. Generally, additional protons are expected to be associated with the low-oxidation model and were not fully investigated until now. Here we consider structural features of the S-0 and S-1 states using a quantum mechanics/molecular mechanics (QM/MM) method. We systematically alter the hydrogen-bonding network and the protonation states of bridging and terminal oxygens and His337 to investigate how they influence Mn-Mn and Mn-O distances, relative energetics, and the internal distribution of Mn oxidation states, in both high and low-oxidation state paradigms. The bridging oxygens (O1, O2, O3, O4) all need to be deprotonated (O2-) to be compatible with available structural data, whereas the position of O5 (bridging Mn3, Mn4, and Ca) in the XFEL structure is more consistent with an OH- under the low paradigm. We show that structures with two short Mn-Mn distances, which are sometimes argued to be diagnostic of a high oxidation state paradigm, can also arise in low oxidation-state models. We conclude that the low Mn oxidation state proposal for the OEC can closely fit all of the available structural data at accessible energies in a straightforward manner. Modeling at the 4 H+ protonation level of S-1 under the high paradigm predicts rearrangement of bidentate D1-Asp170 to H-bond to O5 (OH-), a geometry found in artificial OEC catalysts.