Ca 3 Co 2 O 6 is the archetype of a ferromagnetic 1D Ising compound having antiferromagnetically coupled chains distributed on a triangular lattice. In this paper, we investigate a first-order transition, not detected previously, which takes place along the transformation from the spin-density-wave to the ferrimagnetic state. This T*(H) line has been derived from magnetization and specific heat measurements recorded vs T and vs H, with the magnetic field applied along the anisotropy axis on a set of single crystals. The entropy jump ∆S at the transition has been derived from both the specific heat and magnetization data. A direct link between ∆S and the period of the underlying spin modulations in the SDW state has been established. All the results about T*(H) are compared to the recent theoretical predictions of Kamiya [PRB 107, 134409 (2023)], and the degree of consistency was evaluated from the derived values of the magnetic interactions. Comparisons to similar transitions in related materials are also discussed.