Aerogel films are interesting as coatings due to their unique properties including high surface area, sorption capacity and insulating properties. To date, silica-based aerogel films have been most widely explored due to their ultrahigh surface areas and well-known chemistry. However, the fragile nature of silica aerogels coupled with the limited control over film thickness and dimensions when using traditional deposition techniques limits their use in applications requiring films with good mechanical stability (e.g., in flexible devices). To address these challenges, we present a pressure-aided freeze casting method to pattern, on a variety of substrates (e.g., glass or flexible polyethylene terephthalate), mechanically robust aerogel films composed of covalently cross-linked cellulose nanocrystals (CNCs) with controlled dimensions and internal morphology. To accomplish this, a film of the desired aerogel thickness was deposited on the substrate and a mold with the specific shape for the aerogel was fabricated by xurography (>1 mm lateral dimensions, 7–85 μm thickness) or photolithography (2–500 μm lateral dimensions, 3 μm thickness). An aqueous gel of reactive CNCs or CNCs with poly(oligoethylene-glycol-methacrylate) was drop cast onto the substrate, and pressure was applied so that the gel adopted the mold shape. The gel was subsequently frozen and lyophilized, and the mold was lifted off the substrate, leaving behind patterned porous aerogel films, which were first explored as cell culture scaffolds. Human prostate cancer cells strongly adhered to the aerogels, where individual cells could be isolated on small aerogel arrays while cell clusters were obtained on larger arrays. This system has potential applications in studying single-cell phenotype and developing miniaturized cell-based assays. The simplicity of this freeze casting and lift-off patterning technique makes it attractive for the fabrication of cellulose-nanocrystal-based aerogels with a variety of compositions for applications requiring materials with high surface area, low density, and good mechanical stability.