The morphologies of Cs-neutralized poly(styrene-ran-methacrylic acid) (Cs-SMAA) random ionomers have been studied using scanning transmission electron microscopy (STEM). The Cs-SMAA ionomers exhibit Cs-rich aggregates in the shape of spherical shells that are randomly distributed in a polystyrene-rich matrix. For simplicity, we refer to these as vesicular aggregates. The vesicular aggregates are typically 5-20 nm in diameter and have shell thicknesses of similar to3 run. The vesicular aggregates persist after annealing with their dimensions and number density unchanged. The aggregate diameters and shell thicknesses are independent of the copolymer concentration during neutralization and the rate of neutralizing agent addition. We also demonstrate that our specimen preparation for STEM (microtomy parameters and storage conditions) avoids substantial changes to the bulk ionomer morphology. Overall, the microstructures of the current materials are similar to those recently reported in sulfonated polystyrene ionomers solution-neutralized with Zn.