Chiral helimagnetism is a promising state of matter for next-generation computing devices due to their topologically nontrivial spin textures and tunable magnetoresistance. Considering that the helical spin structure contributes to the mesoscale electrical transport properties, it is imperative to examine and visualize helical magnetic domains and domain boundaries over the characteristic dimensions of electronic devices. Here, we investigate a chiral helimagnet Cr_1/3NbS₂ using second harmonic generation (SHG) wide-field imaging and scanning microscopy. Above the magnetic critical temperature T_C, wide-field SHG microscopy captures the existence of two chiral structural domain states that are related by the spatial inversion symmetry. Below T_C, the symmetry-resolved SHG measurement reveals an unexpected rotational symmetry breaking for the helimagnetic phase, and moreover, visualizes in total six helimagnetic domain states that are related by the three-fold rotation and vertical mirror symmetries. Furthermore, spatially resolved investigation directly shows the interlocking between the structural chirality and magnetic helicity. Finally, we will discuss the origin of observed helical magnetic domain states, which is ascribed to enhanced magnetic anisotropy at the surface, and their potential impact on the electric properties.