Lignocellulosic aerogels were prepared directly from whole biomass Douglas fir wood without prior removal of hemicellulose and lignin using lithium bromide (LiBr) molten salt hydrate (lithium bromide trihydrate, LBTH) as a cellulose solvent via a procedure of cellulose dissolution, gelation, and regeneration. The fabricated aerogels had a homogeneous and continuous porous structure, extremely high porosity, large surface area, and very low density. The lignin-excluding aerogel had a density as low as 4.6 mg/cm3 and a porosity larger than 99%, while the lignin-including whole biomass aerogel retained almost all lignin and more than 90% of the starting biomass and had 24.9 mg/cm3 density and 98.3% porosity. A mechanistic study revealed that different from that in other cellulose solvent systems, cellulose gelation and regeneration occurred in two independent steps in the LBTH system. The weak cross-linking through a coordination effect between a cellulose hydroxyl group and Li+ cation when cooling the cellulose solution in the LBTH led to gelation, while cellulose regeneration via precipitation/aggregation due to the exchange of solvent LBTH with nonsolvent water during washing resulted in the formation of a 3D fibrous network of cellulose skeleton.