The primary goal of this thesis is to evaluate vibration control of an all-clamped plate having an unknown disturbance. The vibration control is implemented using a piezoelectric actuator placed at an optimal location. The first part of this thesis considers a robust actuator placement with respect to varying spatial distributions of disturbances. The treatment here, is different from performance-based LQR approaches, since it is based on minimizing the effect of the disturbance distributions. The second part of this thesis addresses a more general case where the plate is under an unknown disturbance. An unknown disturbance is also characterized by the case where the disturbance signal moves randomly over the entire spatial domain. An optimal switching controller algorithm is developed, based on LQR performance, which switches between piezoelectric actuators employed for the vibration control of the plate. A single actuator is selected from the various actuator locations during each time interval, which leads to performance enhancement.