Cotton fiber-reinforced polymer composites have emerged as promising sustainable structural materials. However, the combined influence of fiber volume fraction ($V_f$) and fiber orientation on their mechanical performance has not been fully quantified. In this study, the mechanical behavior of cotton fiber-reinforced epoxy composites containing fiber volume fractions ($V_f$) of 20 vol.%, 40 vol.%, and 50 vol.% was systematically investigated through finite element analysis using ANSYS. Two representative reinforcement architectures, namely unidirectional and tri-directional fiber orientations, were modeled to evaluate their responses under tensile, flexural, and compressive loading conditions. The mechanical performance was assessed to elucidate the reinforcing mechanisms associated with different fiber configurations. It was found that the mechanical properties were consistently enhanced as the fiber volume fraction increased. Among all configurations, the composite containing 50 vol.% fiber volume fractions with a tri-directional orientation exhibited the highest mechanical performance, achieving tensile, flexural, and compressive strengths of 57.67, 71.03, and 68.31 MPa, respectively, corresponding to improvements of 46.1%, 17.5%, and 16.1% over the 20 vol.% tri-directional composites. Similarly, the 50 vol.% unidirectional composite demonstrated increases of 43.4% in tensile strength, 15.2% in flexural strength, and 17.3% in compressive strength relative to the corresponding 20 vol.% unidirectional configuration. Superior mechanical performance was consistently achieved by the tri-directional architecture compared with the unidirectional counterpart, which was attributed to a more uniform stress transfer mechanism, reduced stress concentration, and improved load redistribution, as confirmed by the von Mises stress distributions obtained from the finite element simulations. These findings demonstrate that both fiber volume fraction and fiber orientation play critical roles in governing the mechanical behavior of cotton fiber-reinforced epoxy composites. The numerical results further indicate that optimizing reinforcement architecture can substantially improve structural efficiency while maintaining the inherent sustainability and lightweight characteristics of natural fiber composites, thereby supporting their broader application in environmentally responsible engineering structures. 20%, 40%, and 50%.