Described is a corner extension mounting system used to secure a net system to buildings or structures that have obstructions such as corners. The corner extension mounting system easily and quickly attaches to a floor beam or other structure around the perimeter of a building or structure. The corner extension mounting system includes a mounting bracket, a corner extension, a support bracket, and a cantilever arm. The mounting bracket is adjustable and also reinforces the corner extension and the support bracket. The support bracket attaches to two cantilever arms that are positioned perpendicularly around the corner of a building. The cantilever arms are attached to the support bracket with pivot pins that allow the cantilever arms to rotate. A debris net is suspended between the upper end of the cantilever arm and the building. Among other things, the corner extension mounting system allows for easy installation of a net system around a building or structure undergoing construction or maintenance.