The magnetic Ln$\mathrm{<mrow\; data-mjx-texclass="ORD">3+</mrow>}$ ions in the fergusonite and scheelite crystal structures form a distorted or stretched diamond lattice which is predicted to host exotic magnetic ground states. In this study, polycrystalline samples of the fergusonite orthotantalates $M$-LnTaO$4$ (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) are synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. TbTaO$4$ orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with $k\to =0$, magnetic space group 14.77 ($P21$$\prime /c$) and Tb moments parallel to the $a$-axis. No magnetic order was observed in the other materials studied, leaving open the possibility of exotic magnetic states at K.