Monoclinic Li₃Co₂SbO₆ has been proposed as a Kitaev spin liquid candidate and investigated intensively, whereas the properties of its polymorph, the orthorhombic phase, are less known. Here we report the magnetic properties of orthorhombic Li₃Co₂SbO₆ as revealed by dc and ac magnetic susceptibility, muon spin relaxation (μSR), and neutron diffraction measurements. Successive magnetic transitions at 115, 89, and 71 K were observed in the low-field dc susceptibility measurements. The transitions below T_N (115 K) are suppressed at higher applied fields. However, zero-field ac susceptibility measurements reveal distinct frequency-independent transitions at about 114, 107, 97, 79, and 71 K. A long-range magnetic ordered state was confirmed by specific heat, μSR, and neutron diffraction measurements, all indicating a single transition at about 115 K. The discrepancy between different measurements is attributed to possible stacking faults and/or local disorders of the ferromagnetic zigzag chains, resulting in ferromagnetic boundaries within the overall antiferromagnetic matrix.