This article reports the electrochemical double layer behavior at the interfaces of ionic liquids (ILs) and a boron-doped diamond (BDD) electrode as measured by large-amplitude Fourier transformed alternating current (AC) voltammetry (FT-ACV). Data are collected over a ≥2 V potential range and fitted to a simple resistor-capacitor circuit model. The absence of significant higher-order AC harmonic components implies nearly ideal capacitive behavior in the potential ranges examined. Capacitance values for two protic ILs and three aprotic ILs range from 3 to 8 μF cm-2 and generally increase (1-2 μF cm-2 V-1) as the potential is swept from negative to positive values. Capacitance-potential data display little dependence on the composition of the IL. The generally featureless, linear dependence of capacitance on potential over a wide potential range is similar to that reported for BDD electrodes in aqueous electrolyte media, suggesting that the BDD electrode is largely insensitive to the nature of the electrolyte media. The present study concludes that FT-ACV affords an efficient approach to probe the IL-electrode interface, with minimal capacitive hysteresis based on the potential scanning direction.