A number of composition dependent physicochemical properties were measured for the water-[C(4)mim][MeSO3] binary system at 85 degrees C. Specifically, we provide data for density, heat capacity, heats of dissolution, conductivity, viscosity, as well as the self-diffusion coefficients of the cation, anion, and water. Ionic liquids based on the MeSO3 anion constitute a suitable medium for various chemistries. This study addresses the need to provide physicochemical data on [C(4)mim][MeSO3] and the water-[C(4)mim][MeSO3] binary systems that are currently unavailable. Additional analysis of the combined data is also presented to provide further insight into the molecular level behavior of the water-[C(4)mim][MeSO3] binary system.