A series of Li-, Na-, and Cs-neutralized polyester ionomers with well-defined poly(ethylene oxide) (PEO) spacer lengths between sulfonated phthalates have been investigated by X-ray scattering at room temperature. As the spacer lengths are increased the PEO segments crystallize, as evidenced by multiple crystal reflections that are identical to those of pure poly(ethylene glycol) oligomers. This crystallization also produces multiple small-angle peaks, which correspond to the well-defined thickness of PEO crystallites. The ionomer peak (q = 1-5 nm(-1)) is absent in the Na- and Cs-neutralized ionomers, while the Li-neutralized ionomers show peaks at q = 2-3 nm(-1), reminiscent of conventional ionic aggregates in ionomers. Detailed analysis of the normalized X-ray scattering intensity from these ionomers reveals a variety of ionic states that are highly dependent on the cation size. The states of ionic groups change from a majority of isolated ion pairs to aggregated structures as the cation size decreases from Cs to Li. These findings compare favorably with ab initio calculations.