Hansen solubility parameters (HSPs) are useful in investigating the affinities among two or more components. Here, we propose a new method for determining the HSPs of ionic liquids (ILs), with a focus on ionic dissociation estimations from Walden plots of IL-organic solvent solutions. We investigated ILs with different cation and anion structures, that is, phosphonium ammonium; imidazolium; and pyridinium cations and bis(trifluoromethanesulfonyl)imide ([TFSI](-)), trifluoromethanesulfonate ([TfO](-)), and hexafluorophosphate (PF6-) anions. The Hansen spheres determined from Walden plots (the Hansen ionicity spheres) became smaller than the Hansen solubility spheres, which ensures highly accurate HSP values. Each calculated HSP of an IL was independent and corresponded to the solvatochromic parameters and previously reported values.