Polymer-grafted nanoparticles stabilized in ionic liquid (IL)-solvent mixtures are investigated by using transmission electron microscopy, dynamic light scattering, and electrochemical impedance spectroscopy. The ionic conductivity of IL-solvent mixtures with the polymer-grafted nanoparticles is found to be higher than that of nanoparticles in the IL. These particles offer additional interactions between polymer and IL, which can mitigate solvation in ILs with solvents. Motivated by this, we present the conductivity data of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM-TFSI) with poly(methyl methacrylate) (PMMA)-grafted particles in good and bad solvents and further discuss how graft density influences the swelling of PMMA and solvation characteristics of HMIM-TFSI. We found that HMIM-TFSI-acetonitrile containing high grafting density particles has a higher conductivity than that of the HMIM-TFSI-methanol mixture with grafted particles. Thus, solubility of PMMA in acetonitrile and preferential interactions between PMMA-HMIM-TFSI are shown to govern the swelling, solvation, and conductive properties of IL with the polymer-grafted nanoparticles.