The CS molecule has been studied with constant ionic state (CIS) spectroscopy in the photon energy range 11.2-19.5 eV using radiation from a synchrotron source. The spectra were obtained by monitoring the intensities of the first three vibrational components in the first photoelectron band as a function of photon energy, The structured spectra obtained have been analyzed in terms of excitation to and autoionization from Rydberg states with A (2) Pi, B (2) Sigma(+), and C (2) Sigma(+) ionic cores. Photoelectron spectra of the first band of CS recorded at selected resonant energies showed extended vibrational structure which was used to obtain improved ionic state vibrational constants for CS+ X (2) Sigma(+) compared to those derived from an off-resonance spectrum.