In situ ellipsometry was used to study the electrodeposition of the viologen-based redox polymer formed by electroreduction of N,N’-bis[-3-(trimethoxysilyl)propyl]-4,4’-bipyridinium dichloride (I) at Pt electrodes. The importance of dimerization of the 1+ species in the film was demonstrated by comparing voltammetric results for thin films of the polymer with equations derived for the current, peak potential, and Limiting shape of thin layer, linear sweep voltammograms for a kinetically reversible couple, where one form of the couple undergoes fast reversible dimerization. The complex refractive index and viologen concentration for solvent swollen films were determined for the 2+ and 1+ states of the viologen groups during film growth. The polymer deposited isotropically to thicknesses of less than or equal to 400 nm (2+ state). High quality films for ellipsometric measurements were also formed by spin-coating the electrode with ethanolic solutions of I. The film optical constants, degree of film swelling by solvent sorption, and changes in swelling associated with reduction in blank electrolyte solution were determined from least squares analysis of data for multiple angles of incidence, without resorting to auxiliary measurements. Reduction caused film shrinkage of about 25%. Modeling of transient ellipsometric data for large potential steps was used to test the theory that electron transport represents a diffusion process. Theoretical curves were calculated by treating the film as a system of stratified layers whose optical constants were given by effective medium theory using the refractive indexes of completely reduced and oxidized films and simulated thin layer conversion profiles (i.e., gradients) for diffusional transport. During film reduction, hopping of electrons (between 1+ and 2+ centers) effectively followed a diffusion model, with reduction proceeding outward from the electrode/film interface. Film oxidation back to the 2+ state was slower and required film reswelling, which lagged the extent of oxidation during both fast and slow conversions (i.e., during potential steps and sweeps). Ellipsometric data provided the first direct evidence that film expansion driven by a redox process can impede charge transport.