The low-temperature magnetic ordering of the dimorphic DySi compound has been studied at 1.5 K by neutron diffraction on two polycrystalline samples. The samples comprise various amounts of the two orthorhombic modifications: CrB-type ( Cmcm Nr. 63, all atoms at 4 c site: ( 0, y, 1 4 )) and FeB-type ( Pnma Nr. 62, all atoms at 4 c site: ( x, 1 4 , z)), both order antiferromagnetically ( T N≈38 K). The CrB-type phase orders with a uniaxial structure with the wave vector q 1=(0, 0, 1 2 ) requiring a doubling of the c-axis. The Dy moments point along the linear chain with the shortest distance c. At 1.5 K, the ordered moment value is 8.57(1) μ B/Dy atom. Two symmetry independent wave vectors describe the 1.5 K magnetic ordering of the FeB-type phase: q 2=(0, 1 2 , 1 6 ) and q 3=(0, 0.484(1), 0.0892(1)), coexisting in form of domains. In both structures the magnetic moments are confined to the (0 0 1) plane at an angle of 2(2)° and 22(3)° from the shortest axis b, respectively. Both structures correspond to sine wave modulations. The amplitude of the q 2 wave is m o =7.5(1) μ B/Dy atom and that of q 3 8.2(1) μ B/Dy atom. The wave vector q 2 when referring to the ( a, 2 b, c) cell and the wave vector q =(0, 0, 1 6 ) corresponds to a transversal modulation, which by a proper origin choice can be also described as an antiphase domain structure with two amplitudes. The moments point to the b-axis and are stacked in the sequence (+ m o /2, − m o /2, − m o , − m o /2, + m o /2, + m o , …) along the c-direction, while t b acts as an antitranslation. For the q 3 phase, the local moment value depends on the atom position in the wave. We also discuss the case where q 3 and q 2 act simultaneously in physical space.