There is considerable interest in understanding ion transport in charged polymeric materials for applications in energy storage. In this work, all-atom molecular dynamics simulations and experimental measurements are combined to study ion mobility in poly(2-vinylpyridine) (P2VP) functionalized with N-methylpyridinium iodide (NMP+I-)-a system of particular interest due to its amenability in applications involving directed self-assembly. Experimental measurements demonstrate that increasing water content tends to decrease the glass transition temperature and enhance ion conductivity. While the simulations demonstrate similar trends, further analysis reveals that increasing water content also promotes ion-water interactions, which leads to overall shorter ion-polymer association times and thus enhanced ion mobility. Meanwhile, both the experimental measurements and the simulations demonstrate that decreasing the degree of NMP functionalization also enhances polymer-chain relaxation; however, the faster polymer dynamics negligibly affect I- mobility, at least in dry systems where the overall rates of ion transport are very low. Overall, these results highlight the importance of water in facilitating I- diffusion in these systems and provide insights into the impact of water content and NMP functionalization on polymer relaxation behavior. These results should be useful for identifying more effective polymer architectures and processing criteria in future charged polymeric materials.