Five microwave interferometers are used to measure radial and longitudinal electron density profiles versus time in the 2XII minimum-B mirror containment experiment. The mean plasma radius determined from a radially offset interferometer agrees with electrostatic probe and laser measurements. The longitudinal profile is consistent with a collisional ion angular distribution with a density at the mirrors of approximately 5% of the central density. After compression the plasma shape remains approximately constant. Plasma densities beyond the mirrors were less than 5% of the central density.