We hypothesize that the electrolyte-dependent differences in electrochromic properties of hexagonal cesium tungsten oxide are the result of different electronic states that result from the intercalation sites occupied during electrochemical reduction. Based on the optical and XPS data, the intercalation of potassium, which is expected to be to the hexagonal tunnels in the material, coincides with the injection of free electrons. These electrons expand the plasmonic volume within each NC, resulting in the increased extinction of the LSPR, a response which is almost identical to that for films reduced in an electrolyte containing TBA + . Charging with TBA + -based electrolytes is capacitive and gives rise to an increased population of free electrons. The spectral change in films reduced in these two electrolytes is consistent with a purely plasmonic modulation of the extinction. The optical response to intercalation of the two smaller cations deviates from the LSPR line shape, which we ascribe to the formation of polaronic states due to intercalation into interstitial sites inaccessible to larger cations. We hypothesize that the ability of these smaller cations to diffuse through the square channels and occupy sites within these voids leads to visible light electrochromism. The similar capacities observed in lithium and sodium electrolytes point to the same type of intercalation sites being accessible. The coloration efficiency, which is the amount of optical density change per unit of injected charge, is also dependent on the electrolyte cation used. The coloration efficiency at longer wavelengths in the NIR is similar across all electrolytes, with only lithium showing a slightly higher coloration efficiency, which could be related to its expected ability to diffuse through the small trigonal channels in the material or the ability to more readily diffuse around cesium cations blocking pathways through the hexagonal channels. In the visible range, the coloration efficiency is substantially different between the smaller cations (Li + and Na + ) and the larger cations (K + and TBA + ).