Microelectrode arrays are important tools that enable a wide range of neuroscience experiments, as well as emerging medical applications of neuroprosthetics and neuromodulation. Information on noise, impedance, charge injection capacity, stability, and the quantity of electroactive material on an electrode surface is is important for system optimization and are typically acquired using potetionstats. This report describes the design and in vivo test results of an electrochemical potentiostat system that rapidly multiplexes through electrodes, reducing measurement time for impedance spectroscopy ~4x at frequencies relevant to neural signals (<7.5 kHz).