Advanced district thermal energy systems operating at near-ambient water temperatures have the potential to reduce source energy use intensity for heating and cooling 21-25% relative to code-compliant, building level systems. However, these systems face barriers to adoption, including the very large number of potential network configurations. To address this barrier, a network topology optimization framework for district thermal energy systems has been developed. The framework has been applied to a prototypical urban district for illustrative purposes, and identified solutions with life cycle cost values 14% to 72% lower than that of base case scenarios based on conventional design approaches, depending on the base case scenario selected.