The evolution of structure in a quiescent electrorheological fluid was monitored by following the increase in static permittivity after an electric field was applied. The zero-time permittivity agreed well with theoretical predictions for a randomly dispersed colloidal suspension. As time progressed, the permittivity increased as the anisotropic structure evolved, and the rate of increase in permittivity at early times depended on the square of the applied field. For low particle loadings and high fields, the measured permittivity at long times agreed with predictions for dense columnar aggregates. Under lower applied fields or in more concentrated suspensions, however, the intermediate time coarsening process was quenched, and the corresponding final structure was less compact, resulting in a lower permittivity than predicted.