In the title compound, [Co(C(7)H(5)O(3))(C(14)H(12)N(2))(H(2)O)(2)]NO(3)·2H(2)O, the Co(II) ion is six-coordinated by two N atoms of a 2,9-dimethyl-1,10-phenanthroline (dmphen) ligand, two carboxyl-ate O atoms of one 4-hydroxy-benzoate anion and two O atoms of two water mol-ecules, in a distorted octa-hedral environment; the two water mol-ecules occupy the apical positions. In the crystal structure, the ionic units and water mol-ecules are linked through O-H⋯O hydrogen bonds, leading to the formation of a three-dimensional network. In addition, π-π inter-actions between a pyridine ring of the dmphen ligand and the benzene ring of the hydroxy-benzoate anion [centroid-centroid separation = 3.6861 (3) Å] are observed.