The crystal structures of three hydrogen-bonded co-crystals of 4-alkoxybenzoic acid–1,2-bis(pyridin-4-yl)ethane (2/1), namely, 2C9H10O3·C12H12N2, (I), 2C10H12O3·C12H12N2, (II), and 2C11H14O3·C12H12N2, (III), have been determined at 93, 290 and 93 K, respectively. In (I), the asymmetric unit consists of one 4-ethoxybenzoic acid molecule and one half-molecule of 1,2-bis(pyridin-4-yl)ethane, which lies on an inversion centre. In (II) and (III), the asymmetric units each comprise two crystallographically independent 4-alkoxybenzoic acid molecules and one 1,2-bis(pyridin-4-yl)ethane molecule. In each crystal, the two components are linked by O—H...N hydrogen bonds, forming a linear hydrogen-bonded 2:1unit of the acid and the base. Similar to the structure of 2:1 unit of (I), the units of (II) and (III) adopt nearly pseudo-inversion symmetry. The 2:1 units of (I), (II) and (III) are linked via C—H...O hydrogen bonds, forming tape structures.