In the title co-crystal, C5H9N2+·C6H5O3S−·C5H8N2, the two 1,2-dimethylimidazole rings exist as partially protonated moieties in the asymmetric unit as a two-part disordered unit wherein the acidic hydrogen atom is bound to each ring. The two imidazolium cations share a strong hydrogen bond via the acidic hydrogen atom, which is disordered between two positions, being bonded to the first versus second imidazole ring in a 0.33 (2) to 0.67 (2) ratio. A benzene sulfonate anion is present for charge balance and interacts with the aromatic H atoms on both imidazole rings as well as with the methyl groups on the rings.
