A highly segmented aerogel Cherenkov detector has been designed and constructed for use in measurements of inclusive and semi-exclusive particle production in 15 GeV/ c per nucleon nucleus-nucleus collisions. The counter consists of 96 separate cells of refractive index n = 1.02 aerogel. A diffusion box is utilized to transport the Cherenkov light to 5 in. phototubes. Light yields in excess of 8 photoelectrons have been obtained.