The title compound, [Co(C(18)H(23)N(10))](BF(4))(2) x H(2)O, is the result of complexing a Co cation (initially in a Co(II) state) with tris[2-(1H-imidazol-2-ylmethyleneamino)ethyl]amine (L), obtained by a condensation process involving imidazole-2-carbaldehyde and tris(2-aminoethyl)amine. Both the Co cation and the ligand were modified in the synthesis process, the cation via oxidation to Co(III), and the ligand via deprotonation to convert it into the 2-(2-{bis[2-(1H-imidazol-2-ylmethyleneamino)ethyl]amino}ethyliminomethyl)imidazolide anion (L(-)). The ligand chelates the metal centre in a hexadentate fashion, forming a slightly distorted octahedral CoN(6) chromophore. Packing is governed by N-H...N hydrogen bonds defining zigzag chains. A similar structure in the literature is discussed, and the wrong assignment of the oxidation state, given therein to the Co cation, is corrected.