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In contemporary batteries, solid polymer electrolytes are widely prioritized for their easy processability and safety; however, they suffer from limited ionic conductivity. Polymerized ionic liquids (PILs) counter this shortcoming by combining mechanical properties of polyions while allowing the counterions (anions) to maintain their free mobility. Poly(1-vinylimidazolium bistriflimide)-grafted iron oxide (Fe3O4) nanoparticles with different chain lengths were synthesized to investigate the effect of grafting the PIL chains on the ionic conductivity. The long-range Coulombic interactions among PIL-grafted chains assist the formation of nanoparticle strings that percolate even at low particle concentrations. Within the percolated network, the connectivity of polycation grafts enabled effective ladder-like ion hopping of TFSI–anions and the cooperative ion motion in nanoparticle networks. The self-assembling nature of nanoparticles, when grafted with polymer electrolyte chains, increased ionic conductivity by promoting the facilitated transport of counterions. Upon incorporating ionic liquid to the PIL-grafted nanoparticles, the presence of ionic clustering was observed to decrease conductivity. Our results demonstrate that the graft chain confinement and particle percolation are essential factors for single-ion conductor design.