More than half of occupant lower extremity (LEX) injuries due to automotive frontal crashes are in the knee-thigh-hip (KTH) complex. To design the injury countermeasures for the occupant LEX, first the biomechanical and injury responses of the occupant LEX components during automotive frontal crashes should be known. The objective of this study is to develop a detailed biofidelic occupant LEX Finite Element (FE) model based on the component surfaces reconstructed from the medical image data of a 50th percentile male volunteer in a sitting posture. Both volumetric (unstructured) and structural mesh methods were used to generate the solid elements (mostly hexahedral type) to enhance the model simulation accuracy. The FE model includes the femur, tibia, fibula, patella, cartilage, ligaments, menisci, patella tendon, flesh, muscle, and skin. The constitutive material models and their corresponding parameters were defined based on literature data. The femur model was validated against the dynamic three-point bending and the quasi-static femur head compression tests. The leg model, including tibia and fibula, was validated against the combined axial compressive and bending loading tests. The predicted femur shaft three-point bending impact force time history, femur head compressed peak fracture force magnitude and the corresponding fracture location, and leg bending moments showed a good correlation with the test corridors and matched the test fracture locations well.