The tuning of magnetic properties through electrochemical loading of hydrogen has recently attracted significant interest as a way to manipulate magnetic devices with electric fields. In this paper we investigate quantitatively the magneto-ionic effect of hydrogen uptake on the magnetic properties of rare-earth transition-metal alloy Tb𝑥Co(100−𝑥) in the composition range of 𝑥=10−39at.% using ion implantation. Using this technique we are able to link changes in magnetic behavior to exact concentrations of hydrogen, isolated from the movement of any other ions that would be a factor in electrochemical studies. The composition of the alloy has been varied alongside the hydrogen dose to characterize the effect of progressive hydrogen loading on the full range of 𝑥displaying out-of-plane magnetic anisotropy. We find large changes in two important properties: the compensation composition and the Co-rich in-plane to out-of-plane magnetic anisotropy transition composition, both of which move by 6 at.% toward higher Tb concentrations after hydrogen implantation. This shift in composition does not increase with a larger dose. From the changes in magnetization we attribute the change in compensation composition to a significant reduction of the moment on the Tb sublattice.