The dynamics of chain and ionic group motion were investigated in a series of ethylene-methacrylic acid (E/MAA) ionomers of varying cation type and neutralization level, all formed from the same E/MAA copolymer. Low-shear-rate rheological measurements were utilized to determine the terminal relaxation time (t(d)) of the polymer chains. The much faster ion-hopping time (tau) was measured through the use of cation diffusion studies, in which a finite slab of one ionomer diffuses into a matrix of a second ionomer. For the Mg/Ca, Mg/Li, Na/Ca, and Na/Li diffusion couples studied, the diffusion coefficient follows inversely with melt viscosity, though tau extracted from the diffusion coefficients depends more weakly on cation type than does t(d) obtained from melt rheometry. For the highly neutralized E/MAA ionomers, tau is 4 orders of magnitude shorter than t(d), but the two relaxation mechanisms have a similar dependence upon temperature, in agreement with current theories of ionomer dynamics.