The elevated levels of tree mortality attributed to mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) in western North American forests create forest management challenges. This investigation introduces the production of submicron or nanometer lignocellulose fibrils for value-added materials from the widely available resource represented by dead pines after an outbreak. Lodgepole pine (Pinus contorta Dougl. ex Loud.), trees from two different times since infestation and a noninfested live tree as a control were used for mechanical fibrillation. Fiber deconstruction down to the micro-/nanoscale from infested wood was performed using mechanical fibrillation, without any chemical (pre)treatment. The effects of fibrillation were monitored as a function of processing time, and the respective products were characterized. The changes in fibril morphology, cellulose crystallinity, water retention value, and cellulase adsorption capacity were determined. Interestingly, no significant differences were found between fibrillated samples from the live and the MPB-killed trees. It can be concluded that MPB-killed lodgepole pine is a suitable feedstock for the production of lignocellulose micro-/nanofibrils.