Wind energy is proving to be a promising energy source to complement conventional energy systems in meeting global energy demands, and is currently one of the fastest growing renewable energy sources. Modern wind turbines are large, flexible structures operating in uncertain environments. Power capture and economic value increase with turbine size, leading to steadily increased turbine size over the last three decades. Along with larger size comes intensified structural loads, presenting challenges in mechanical system design. One of these challenges is the dynamic deflection of structural components. These passive system dynamics interact with the active control of wind turbine energy generation. Because of this interaction, addressing the physical and control system design of these devices in a comprehensive manner is vital to ensuring maximum energy extraction, system reliability, and other critical metrics. A large portion of existing work has aimed to increase energy production through optimal control system design (through some combination of rotor speed and pitch control). This strategy treats physical system design as a fixed entity, overlooking potential gains. Further performance increases can be realized through a broader systems approach where physical and control system design are tackled simultaneously. This approach, known as co-design, can capitalize on the synergy that exists between passive system dynamics and active control to increase performance further. In this article a new method for wind turbine design is presented that produces system-optimal results by accounting for the coupling between plant system and control system design. A case study is presented that demonstrates significant performance improvements over conventional sequential design approaches.