Measurements of the electrocaloric effect in crystalline Rochelle salt throughout the ferroelectric range have been made and have been used to determine the Devonshire "dielectric stiffness" coefficient, the ferroelectric Curie temperatures, and the spontaneous polarization close to both Curie temperatures. The results are shown to be consistent with the thermodynamic properties of Rochelle salt as determined from measurements of the spontaneous polarization and the low-field differential susceptibility.