This phase I trial studies the side effects and best dose of atezolizumab that can be given together with stereotactic body radiation therapy in treating patients with stage I non-small cell lung cancer that cannot be removed by surgery. Monoclonal antibodies, such as atezolizumab, may interfere with the ability of tumor cells to grow and spread. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. Stereotactic body radiation therapy is a specialized radiation therapy that delivers a single, high dose of radiation directly to the tumor and may kill more tumor cells and cause less damage to normal tissue. Giving atezolizumab together with stereotactic body radiation therapy may kill more tumor cells and be a better treatment for non-small cell lung cancer that cannot be removed by surgery.