We propose a liquid crystal (LC) grating with a ternary orientation domain for application to optical polarization measurements. The ternary orientation domain, which generates two-dimensional diffraction properties, is the key to simultaneous acquisition of multiple of polarization parameters. The LC molecular orientation state and the polarization dependence of the diffraction efficiency were investigated experimentally, focusing on the applicability to a practical Stokes polarimeter. An experiment was conducted using the proposed LC grating as a Stokes polarimeter, and the four Stokes parameters (S0, S1, S2, and S3) were determined for linearly and circularly polarized incident light. As a result, the feasibility of the proposed LC grating Stokes polarimeter has been demonstrated experimentally. Finally, the operational performance of the proposed LC grating Stokes polarimeter is discussed using a figure of merit that is numerically derived from the measured polarization dependence of the diffracted light intensity.