The location of extra-framework Cu2+ cations in the dehydrated copper ion exchanged zeolite, ferrierite, has been determined from the analysis of synchrotron X-ray powder diffraction data (Cu-0.023(Al0.065Si0.935)O-2; space group Immm, a = 18.8101(2) Angstrom, b = 14.0930(2) Angstrom, c = 7.44527(7) Angstrom, V = 1973.67(6) Angstrom, Z = 36, R-wp = 9.89%, chi(2) = 1.12). One copper site was found towards the side of the 8-ring window at the intersection of the 10- and 8-ring channels. An electron spin resonance (ESR) spectroscopic study indicates the presence of one Cu2+ species in the hydrated sample, which forms two Cu2+ species upon evacuation to 200 degrees C, only one of which remains after evacuation to 360 degrees C. This remaining Cu2+ species has nonaxial symmetry. The low coordination, but high accessibility of the cation site provides a possible explanation for the high activity of ferrierite and its related pentasil family members for nitrogen oxide decomposition.