A model is presented for radial diffusion and charge state partitioning of sulfur and oxygen ions in the Io torus, including effects of electron impact and charge exchange. When applied to Voyager 1 radial profiles of total ion flux tube content, the model shows that the ion residence time in the torus, &tgr;D, as defined in spectroscopic studies of ion partitioning, is related to the radial diffusion coefficient, DLL, at L=7 by &tgr;D≈8/DLL(7). This result appears to bring spectroscopic estimates of the ion residence time (&tgr;D>60 to 100 days) into reasonable agreement with estimates of DLL from magnetospheric diffusion studies, DLL≈10-6s-1.