A composite reinforced mull post is disclosed for use in an entryway assembly. The mull post may engage a door on one side and a side light window on the other side. The mull post may comprise a one or two piece outer portion and one or more internal reinforcing members. The outer portion may comprise a plurality of interlocking pieces. The pieces may include a stop portion and a support portion, each with interlocking ribs. A first internal reinforcing member may be formed of engineered material such as a wood laminate, and a second reinforcing member may comprise a channel that extends partially around the first reinforcing member. The reinforcing member may include orthogonal portions conterminously received within a correspondingly shaped central chamber formed by the housing formed by the joined interlocking pieces.