An exterior siding mounting bracket is secured to a substructure and projects over siding that covers the substructure. The bracket comprises a base member attached to the substructure and has at least one elongated wall projecting laterally outward from the substructure. A trim member has an outer flange with the siding disposed between the substructure and the outer flange. First and second side partitions project laterally inward with respect to the substructure and from the outer flange for snap fitting to the at least one elongated wall. A water diversion device has a trough located above the first and second side partitions supported by the outer flange and projecting laterally toward the substructure for receiving and diverting water run-off away from the substructure. At least one drainage tube of the water diversion device projects unitarily downward from the trough.