The magnetic ordering of the anomalous antiferromagnet CeSb, which has a NaCl crystal structure, was determined in zero applied magnetic field by means of neutron diffraction investigations of single crystals and powder. Below the Neel temperature TN of (16.1+or-0.1)K, there exist six partially disordered magnetic phases of antiphase domain type ((100) superstructures) with (100) orientation of the magnetic moments. At 4.4K, the ordered magnetic moment equals (2.10+or-0.04) mu B, which corresponds to the free-ion value of 2.14 mu mB for Ce3+. The temperature dependence of the ordered moment shows a first-order phase transition at TN. At approximately TN/2 there is a first-order phase transition to a FCC type IA low-temperature configuration. The unusual magnetic properties of CeSb, which result from anisotropic exchange and crystalline electric field effects, resemble those of certain actinide NaCl-type compounds.