The collective polarizability anisotropy dynamics of liquid methyl iodide at room temperature and ambient pressure was studied by using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) with 45 fs laser pulses. The OHD-RIKES data are analyzed by using both the model-dependent approach, which assumes four distinct temporal responses, and the model-independent Fourier transform approach, which generates a spectral density. Near zero time, the OHD-RIKES transient is dominated by the instantaneous electronic response. The short-time nuclear response is characterized by two components. The first component is interpreted as arising from an inhomogeneously broadened (fwhm approximate to 62 cm(-1)) underdamped intermolecular vibrational mode with a mean frequency of similar to 60 cm(-1). The second component is an intermediate quasi-exponential response with a 1/e time constant of similar to 200 fs. At longer times, the OHD-RIKES transient decays exponentially with a lie time constant of 1.76 +/- 0.05 ps, which corresponds to the collective reorientation time of CH3I. The spectral density peaks at similar to 24 cm(-1) and has a fwhm of similar to 80 cm(-1). The spectral density can be well. fitted by an ohmic distribution function with omega(c) approximate to 30 cm(-1). The spectral density obtained from the OHD-RIKES data is consistent with previously measured depolarized Rayleigh scattering and low-frequency far infrared absorption spectra for liquid CH3I.