The heat capacity of thallium(I) n-octanoate has been measured from 5 to 350 K by equilibrium adiabatic calorimetry and, taken together with DSC data determined earlier by a subset of the present authors, represents the thermodynamic behaviour in the liquid phase at about 500 K. Transitions occur at 269.8, 290.0, and 293.5 K, melting at 411 K, and clearing at 495 K. Except for a small Delta(trs)S(m) degrees, the lowest temperature (269.2 K) phase transition (crystal IV/crystal III) has Delta(trs)S degrees = 0.62 R, the higher temperature transitions (approx. 293.5 and 290 K) have Delta(trs)S(m) degrees values for III/II/I of 3.97 R ((approximate partial resolution) III/II congruent to 1.7 R and II/I = 2.25 R), for crystal I/mesophase (411 K) of 1.66 R, and for mesophase/isotropic liquid (495 K) of 0.73 R.