Low-field magnetic properties of ceramic La_1-xCa_xMnO₃ (0 ≤ x ≤ 0.4) are investigated between T = 5 and 310 K. The paramagnetic-ferromagnetic transition is observed in all the samples. The dependence of the Curie temperature, T_C, on x is described within a model of spin polarons associated with electronic localization. Critical behaviour of the susceptibility χ^-1(T) approx. (T - T_C)^γ is observed for T > T_C, with the critical exponents γ = 1.20 ± 0.05 and γ^* = 1.64 ± 0.06 below and above the composition x ≈ 0.18 corresponding to the Mn⁴⁺ ion concentration c ≈ 0.23, respectively. For the compound with x = 0.3 no temperature hysteresis of the resistivity is observed in magnetic fields between 0 and 8 T. In all the samples the field-cooled and zero-field-cooled magnetizations deviate below T_C, the difference being approximately equal to the thermoremanent magnetization (TRM). Long-time relaxation of TRM in LCMO is observed for time scales up to 10⁴ s. The relaxation rate reaches a maximum near a wait time t_W approx. 10³ s. The time dependence of TRM can be described with a stretched exponential law, as in spin or cluster glasses in conditions where the observation time is comparable with t_W.