Dielectric relaxation of the ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (EMI+ETS-), is studied using molecular dynamics (MD) simulations. The collective dynamics of polarization arising from cations and anions are examined. Characteristics of the rovibrational and translational components of polarization dynamics are analyzed to under-stand their respective roles in the microwave and teraliertz regions of dielectric relaxation. The MD results are compared with the: experimental low-frequency spectrum of EMI+ETS-,obtained via ultrafast optical Kerr effect (OKE), measurements.