In this paper, a robust controller is designed for the load frequency control (LFC) system in an islanded microgrid with multiple synchronous generation systems. This control strategy can be readily applied to an islanded microgrid which consists of renewable distributed generation and energy storage systems. The robust controller proposed in this paper includes multiple local controllers that are designed and optimized independently by using the μ-synthesis technique and D-K iteration algorithm. This controller accounts for the dynamic coupling among the areas of the microgrid without any communication links required among the local controllers. Moreover, the controller is designed to be robust to the variations of different parameters of the microgrid, and hence improves the frequency control performance significantly. Simulation results of a small islanded microgrid with three generators confirm the effectiveness of the controller design approach proposed in this paper.