Temperature-dependent infrared-absorption measurements were performed on the spin orbit and trigonalcrystal-field split levels of the 4 T 1 g cubic-field ground term of Co 2 + (3d 7 ) in the cadmium halides CdX 2 (X: Cl, Br, and I). Besides γ + 4 →γ + 4 and γ + 4 →γ + 5 , 6 electronic transitions, sharp vibronic lines are observed. From temperature-dependent line shift and line-broadening measurements of these lines, electron-phonon coupling parameters were determined. For Co 2 + in CdCl 2 , where the energy separation of the γ + 4 and γ + 5 , 6 levels studied is comparable to the phonon energies, a contribution from direct one-phonon processes needs to be included. Further line-shift measurements were made on Co 2 + pair lines to determine whether the electron-phonon coupling differed for Co 2 + pairs, with no significant difference being observed. The infrared-absorption spectrum for Co 2 + in CdI 2 is reported.