Plant-derived cellulose nanofibrils (CNFs) have shown reinforcing effects in polymer nanocomposites. However, freeze-dried CNFs are foam-like material, namely aerogel, that are challenging to disperse in a polymer matrix. In this work, a liquid infusion process was developed for a CNF/epoxy nanocomposite cross-linked foam structure with alterable properties without damaging the foam structure. Microstructures of CNF/epoxy composite foams with different formulations were evaluated using a scanning electron microscope. Surface morphology showed that the CNF cross-linked fibers were well attached by epoxy resin. All absolute and specific mechanical properties [by normalizing the measured parameters against the measured density (rho)] were investigated. Water resistance and thermal stability of CNF/epoxy composite foams were investigated by water absorption test and thermogravimetric analysis. The concentration of epoxy solution in both tetrahydrofuran (THF) solvents and ethyl acetate (EA) solvents was shown to improve compressive properties and water resistance. The samples fabricated with higher epoxy concentration had higher compressive properties, better water resistance, and better thermal stability. The CNF/epoxy composite foams exhibited compressive modulus and compressive strength up to 175 and 10 MPa, respectively. The water diffusion coefficient of CNF/epoxy composite foams was reduced with an increase in epoxy loading. Further, the CNF/epoxy nanocomposite foams fabricated by the epoxy/THF solution had a more uniform structure and better strength performance than foams fabricated by the epoxy/EA solution, due to the increased solubility of the epoxy in THF compared to epoxy in EA. The glass transition temperature (T-g) was determined by differential scanning calorimetry. The T-g of the nanocomposites was influenced by the CNF/epoxy composition. Therefore, the properties of CNF/epoxy nanocomposite foams can be optimized via changing the solvent and concentration of epoxy resin in solvent.