The asymmetric unit of the title one-dimensional polymeric compound, {[Co(C10H11O2)2(H2O)3]·2H2O} n , contains one CoII cation situated on a centre of inversion, one-half of a coordinating water molecule, one 2,4,6-trimethylbenzoate (TMB) anion together with one coordinating and one non-coordinating water molecule; the TMB anion acts as a monodentate ligand. In the anion, the carboxylate group is twisted away from the attached benzene ring by 84.9(2)°. The CoII atom is coordinated by two TMB anions and two water molecules in the basal plane, while another water molecule bridges the CoII atoms in the axial directions, forming polymeric chains running along [001]. The coordination environment for the CoII cation is a slightly distorted octahedron. The coordinating and bridging water molecules link to the carboxylate groups via intra- and intermolecular O - H⋯O hydrogen bonds, enclosing S(6) ring motifs, while the coordinating, bridging and non-coordinating water molecules link to the carboxylate groups and the coordinating water molecules link to the non-coordinating water molecules via O - H⋯O hydrogen bonds, enclosing R 2 2(8) and R 3 3(8) ring motifs. Weak C - H⋯O and C - H⋯π interactions may further stabilize the crystal structure.