Early ferric hydroxide species are important precursors in the formation of corrosion products, yet their atomistic evolution from small molecular aggregates to crystal-like motifs remains poorly understood. In this work, we adapt a robust quantum mechanical conformer-search method developed by Wang and Vasilyev to Fe(OH)3 oligomers and systematically investigate the most stable structures from the dimer to the decamer. For each oligomer size, diverse candidate geometries were generated and optimized, followed by energy- and geometry-based screening to identify the lowest-energy structures and representative low-energy isomers. The calculations reveal pronounced size-dependent stabilization and structural reorganization during oligomer growth, together with clear changes in Fe coordination environments, Fe–O connectivity, and electronic properties. The evolution of hydroxyl-bridged frameworks and Fe–O polyhedral connectivity provides insight into how local bonding patterns develop with increasing oligomer size. In addition, the relative stabilities of the low-energy structures indicate that specific oligomer sizes may act as favorable intermediates during the early-stage nucleation of corrosion products. These results suggest that the aggregation of Fe(OH)3 does not proceed as a simple monotonic growth process, but instead involves preferred structural motifs at specific oligomer sizes. Comparisons with representative crystalline corrosion products further clarify how early Fe(OH)3 oligomers evolve toward bulk corrosion phases. This study provides a molecular-level picture of the initial stages of corrosion-product formation and offers a computational route to bridge molecular corrosion precursors with experimentally observed crystalline products.