Priority-based scheduling strategies are often used to resolve contentions in resource constrained networked control systems (NCSs). Such scheduling strategies inevitably introduce time delays into controls. Considering the coupling between priority assignment and control, this paper proposes a novel method to co-design priority assignments and controls for each control loop in NCSs. The co-design aims to minimize the performance degradation caused by time delays. The priority assignment is determined by a path planning approach to search for optimal priority assignments. Model predictive controllers are designed based on optimizing priority assignments to compute optimal controls. Simulations are presented to show the effectiveness of the proposed method.