The title compound, {[Co(C₂H₅COO)₂(H ₂O)]·H₂O} n, was synthesized by the reaction of cobalt(II) carbonate hydrate with aqueous propionic acid. The structure consists of polymeric infinite linear chains with composition [Co(C₂H ₅COO)_4/2(H₂O)_2/2] running along [010]. The chains are formed by Co²⁺ ions linked with bridging propionate groups and water mol-ecules, with a Co⋯Co distance along the chains of 3.2587 (9) Å. The Co²⁺ ion is six-coordinated in a strongly distorted octa-hedral geometry. The chains are connected to each other by a network of O - H⋯O hydrogen bonds involving solvent water mol-ecules.