In this paper, the design methods of decentralized PID controllers based on decoupled subsystems are proposed for two-input two-output systems. The higher-order decoupled subsystems are reduced into simple dynamics such as first-order plus dead-time or second-order plus dead-time and the dominant poles are placed at desired locations. The well tuned parameters of decentralized PID controllers can be obtained based on the movement of poles to get the desired closed-loop response of the system. A corollary derived from the generalized Nyquist stability theorem is used to ascertain the nominal system stability and to hold robust stability in the presence of the process multiplicative uncertainties. Finally, two simulation examples are provided for the validity and effectiveness of the proposed design methods. It can be observed that the high closed-loop performance is obtained using the proposed methods and it is comparable to recent methods available in the literature.