The design, construction, and calibration of a 2 MeV proton spin polarimeter are described. This polarimeter monitors the beam at the transfer point between the linear accelerator and the Alternating Gradient Synchrotron at Brookhaven National Laboratory. The polarimeter determines the beam polarization to an accuracy of 1% in less than ten minutes real time, for the anticipated beam current and pulse repetition rate of the polarized beam, with a carbon filament target that intercepts 1% of the beam particles. Scattered beam particles are collected at 12 and 16 degrees to determine left-right and up-down asymmetries and detect beam angle deviations.