In microgrid planning, topological design is a critical concern for ensuring certain features such as high reliability in islanded operation. This paper proposes a graph partitioning and integer programming integrated methodology for the optimal loop-based microgrid topology planning while considering the distributed energy resources in the microgrid. The proposed methodology is applied to a microgrid test system and the planning results are discussed. The results demonstrate that the proposed planning methodology is able to accurately and efficiently determine an optimal loop structure for microgrids, and exhibit the potentials for applying the proposed planning methodology in practical microgrid applications.