We report on a comprehensive experimental, numerical, and computational investigation on the concentration dependence of the structural/magnetic properties of Co–Rh alloy films. A sizable perpendicular magnetic anisotropy is achieved by controlling the lattice strain via the Co content. Within the 30–40% range of Co concentrations, an experimental effective magnetic anisotropy on the order of 100 kJ/m3 and a computational uniaxial magnetic anisotropy energy of 567 μeV/atom have been observed. First-principles calculations revealed that the lattice strain promotes a strong d-orbital degeneracy near the Fermi level for 40% of Co concentration, leading to an enhanced magnetic anisotropy energy.