The strong coupling, which is the light-matter interaction, leads to changes in the energy landscape of the chemical dynamics, resulting in the modulation of the reaction pathways. In this study, we achieved strong coupling between dye molecules dispersed in the polymer films and the surface lattice resonance mode, which is excited on plasmonic lattice arrays. In addition, we successfully tuned the coupling strength by introducing the electrochemical potential control method. Reversible decreases and increases in the coupling strength were observed as a result of the reversible electrochemical redox reactions of dye molecules. It is important that the spatial distribution of the molecules coupled to the lattice resonance mode was clarified by using various polymer film thicknesses. Our present electrochemical method for controlling strong coupling states represents a promising method for tuning the light-absorption properties of systems.