The magneto-optical Kerr effect is a striking phenomenon whereby the optical properties of a material change under an applied magnetic field. Though promising for sensing and data storage technology, these properties are typically weak in magnitude and are inherently limited by the bulk properties of the active magnetic material. In this work, we theoretically demonstrate that plasmonic thin-film assemblies on a cobalt substrate can achieve tunable transverse magneto-optical (TMOKE) responses throughout the visible and near-infrared (300-900 nm). In addition to exhibiting wide spectral tunability, this response can be varied in sign and magnitude by changing the plasmonic volume fraction (1-20%), the composition and arrangement of the assembly, and the shape of the nanoparticle inclusions. Of particular interest is the newly discovered sensitivity of the sign and intensity of the TMOKE spectrum to collective metallic plasmonic behavior in silver, mixed silver-gold, and anisotropic superlattices.