The title compound, [Co(CO3)(C12H8N2)2]Cl·5H2O, contains [Co(CO3)(phen)2]+ cations (phen = 1,10‐phenanthroline), chloride ions and five independent non‐coordinated water molecules, four of which show positional disorder. The CoIII atom displays a distorted octahedral geometry, being coordinated by four N atoms of two 1,10‐phenanthroline ligands and two O atoms of the bidentate chelating carbonate group. The crystal packing is consolidated by hydrogen bonds and aromatic π–π stacking interactions between neighboring phenanthroline rings.