Fibrillated cellulose has been frequently used for making nanopapers and thin films. However, limited work has been carried out in the construction of such materials using native lignocellulosic biomass. Making papers from fibrillated biomass allows complete utilization of whole plant material and may reduce chemical and energy consumption. Ultra-friction grinding was used to directly fibrillate knife-milled poplar into micro- to nano-sized biomass fibers. Papers were made using the fibrillated biomass containing nanofibrillated biomass and their mechanical properties were tested. Biomass papers made via press-drying had higher tensile strength than papers made by air-drying. A higher press-drying temperature of 180 °C produced stronger papers than at 150 °C. Guar gum substantially increased the strength of the press-dried papers in comparison to cationic starch. Press-drying increased the thermogravimetric peak decomposition temperature by 13 °C in comparison to air-drying.