Crystal and magnetic structures of the \(x=0.2\) member of La\(_{\rm 0.8-x}\)Tb\(_{\rm x}\)Ca\(_{0.2}\)CoO\(_3\) perovskite series have been determined from the powder neutron diffraction. Enhancement of the diffraction peaks due to ferromagnetic or cluster glass ordering is observed below \(T_C=55\) K. The moments evolve at first on Co sites, and ordering of Ising-type Tb\(^{3+}\) moments is induced at lower temperatures by a molecular field due to Co ions. The final magnetic configuration is collinear F\(_x\) for cobalt subsystem, while it is canted F\(_x\)C\(_y\) for terbium ions. The rare-earth moments align along local Ising axes within \textit{ab}-plane of the orthorhombic \(Pbnm\) structure. The behavior in external fields up to \(70-90\) kOe has been probed by the magnetization and heat capacity measurements. The dilute terbium ions contribute to significant coercivity and remanence that both steeply increase with decreasing temperature. A remarkable manifestation of the Tb\(^{3+}\) Ising character is the observation of a low-temperature region of anomalously large linear term of heat capacity and its field dependence. Similar behaviours are detected also for other terbium dopings \(x=0.1\) and 0.3.