Zn_1−xCo_xO nanoparticles with three different values of ‘x’ (x = 0.05, 0.10, 0.15) were prepared by chemical co-precipitation process without any further heat treatment. The X-ray diffraction studies confirmed the wurtzite hexagonal crystal structure for synthesized Zn_1−xCo_xO nanoparticles. The dislocation density results reveal that there is an increase in the concentration of lattice imperfections with increasing the concentration of Co ions. The true values of lattice constants were calculated by using Nelson–Riley Function (NRF). Further, the average bond length (BL) were also calculated and presented. The optical and magnetic properties of Zn_1−xCo_xO nanoparticles were examined by room-temperature photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM), respectively. The calculated values of magnetic susceptibility for Zn_1−xCo_xO nanoparticles with x = 0.05, 0.10, 0.15 were found to be 9.883×10⁻⁴, 2.29×10⁻² and 2.37×10⁻², respectively.