In this study, magnetic-optical properties of Zn1−xCoxO NCs were modulated with x-content. The optical, structural, morphological, and magnetic properties were investigated by optical absorption (OA), fluorescence (FL), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and electronic paramagnetic resonance (EPR). The XRD and Raman results confirm the growth of Zn1−xCoxO NCs, with x greater than 1.0 having occurred for the formation of the nanocomposite (Co-doped ZnO/ZnCo2O4). The formation of the nanocomposite allows new and exciting optical and magnetic properties. SEM images show inhibition in ZnO nanorod growth with Co-content and formation of ZnCo2O4 NCs. OA and FL spectra have changed with x-content in Zn1−xCoxO NCs. These changes are strongly related to the symmetric environment of the Co2+ ions within ZnO NCs and the formation of ZnCo2O4 NCs. A linear dependence of FL intensity was observed with the x-content in the red-green region. The symmetric environment and the nanocomposite formation also alter the magnetic properties confirmed by EPR. Therefore, Zn1−xCoxO NCs can be a material platform suitable for photonic devices, magnetic-optical devices, or spintronics.