This study investigates the stability and optimum gain settings of Load Frequency Control (LFC) for single area reheat thermal power system. The new Particle Swarm Optimization technique (PSO) is used for optimizing Proportional Integral Differential (PID) controller gain values. The proposed technique can be used for the design of the proper PID controller for load frequency control with the help of different objective functions. Furthermore, extension to the uncertainties in the plant model parameters case is also included to illustrate the effectiveness of the proposed controller in damping power system oscillations that follow disturbances. The uncertainties in the plant model parameters case are emulated by changing turbine time constant, generator time constant, reheater time constant and speed regulator parameters by ±25%. Finally, the enhancement in the dynamic response of the system is verified through simulation results of a system under different operating points and exposed to both small and large disturbances. Time domain analysis is used to demonstrate, the necessity of the proposed controller in suppressing power system oscillations that follow disturbances.