A primary science goal of the WFIRST mission is to conduct, via a microlensing survey towards the Galactic Bulge, a statistical census of exoplanetary systems from 1 AU to free-floating planets with massesgreater than Mars. More specifically, for the nominal baseline WFIRST design and fiducial planet mass function, the expected yield of the microlensing survey is for about 1400 bound exoplanets including about 200 with mass smaller than 3 Earth mass.