The influence of Co(II), Co(II)+Mn(II), Co(II)+Ni(II) co-doping on the structure and crystalline perfection of tris(thiourea)zinc(II) sulphate single crystals grown from an aqueous solution at room temperature by slow evaporation solution growth technique has been investigated. The incorporation of foreign metal into the crystalline lattice was well confirmed by chemical formula determined by single-crystal X-ray diffraction analysis. The intensity variations observed in powder X-ray diffraction patterns and slight shifts in vibrational frequencies in Fourier transform IR indicate the lattice stress. Thermal studies reveal the purity of the material and no decomposition is observed up to the melting point. High-resolution X-ray diffraction studies reveal that Co(II)-doped specimen has no clustering of defects while the Co(II)+Mn(II), Co(II)+Ni(II) co-doped crystals show the presence of structural grain boundaries as a result of crystal stress and strain. The as-grown crystals are further characterized by Kurtz powder technique and dielectric studies. Good transparency in the visible region is observed for all the specimens. Interestingly, in co-doping the host crystal selectively accommodates only one foreign metal ion as revealed by single-crystal XRD analysis.