Cyber-physical systems (CPSs) link cyber infrastructure with physical processes through an integrated network of physical components, sensors, actuators, and embedded computers. CPSs comprise critical infrastructures such as smart electric grids, intelligent water distribution networks, health information networks, smart transportation systems, and smart buildings. Developed countries are entirely reliant on such critical infrastructure, hence the need for rigorous assessment of the trustworthiness of these systems. For example, smart grids utilize computation and communication to improve the efficacy and dependability of power generation, transmission, and distribution. Reliance of almost every other critical infrastructure on electric power and the interdependency between these infrastructure systems places smart power grids among the most critical and complex CPSs. The objective of this research is to develop and validate a comprehensive reliability model for cyber-physical critical infrastructures, focusing on smart power grids, and considering interdependencies among physical processes and the cyber network providing intelligence to the system. Such a model can help in guiding investments to eliminate or alleviate vulnerabilities in and failure mitigation for such critical infrastructures. To verify that the model can be generalized for other CPSs, intelligent water distribution networks are also modeled by simulations.