During investigations into sulfide- and selenide-amination reactions using the aminating agent o-mesitylsulfonylhydroxylamine, the monoclinic, (I), and orthorhombic, (II), polymorphs of ammonium 2,4,6-trimethylbenzenesulfonate, NH4+.C9H11O3S-, have been crystallized. Investigation of the hydrogen-bonding motifs within the two polymorphs shows that both contain N+-H...O- hydrogen bonds between the ammonium cations and the 2,4,6-trimethylbenzenesulfonate anions. Polymorph (I) contains R(4)(4)(12) and R(4)(2)(8) graph-set ring motifs, while polymorph (II) contains the same R(4)(4)(12) ring motif in combination with an R(4)(3)(10) motif. The two hydrogen-bonding patterns result in slightly different packing structures for the two polymorphs, but both are based on a thick-sheet arrangement, in which the NH4+ cations are enveloped between two layers of 2,4,6-trimethylbenzenesulfonate anions. In (I), the aromatic rings of the anions are approximately coplanar, giving parallel sheets, whereas in (II) the sheets are antiparallel and the anions pack in a herring-bone manner within the sheets, with angles of 78.76 (8) degrees between the planes of the aromatic rings.