Redox behaviors of electrochemically active self-assembled monolayers (SAMs) prepared on gold surfaces from ferrocene (Fc)-terminated alkanethiols were investigated in more depth in response to the authors' previous study where ionic liquids (ILs) with bis[(trifluoromethyl)sulfonyl]amide (Tf2N-) anions were found to restrict the oxidation of Fc moieties probably due to a steric hindrance of large-sized anions. The redox behaviors in ILs were compared with those in aqueous solutions containing only Tf2N- as anions. Cyclic voltammograms (CVs) suggested that the use of Tf2N- anions lower the amount of electrochemically responsive Fc-groups by about 20% regardless of whether the electrolyte is aqueous or IL-base. Residual water that is sometimes contained in ILs had no effect on the amount of responsive Fc-groups. We tried to directly monitor the adsorption/desorption of anions associated with the redox cycles of Fc-groups by an electrochemical QCM equipped with a resonator using a separately-excited oscillation method. The QCM exhibited periodic frequency changes, which were quantitatively in agreement with the response amounts determined by the CVs, indicating that synchronous but restricted adsorption/desorption of Tf2N- anions takes place.