Inclusion Criteria:

          -  REGISTRATION STEP 1: Participants must have pathologic (cytological or histological)
             proof of non-small cell lung cancer (NSCLC)

          -  REGISTRATION STEP 1: Participants must have stage III NSCLC with Zubrod performance
             status of 2 or stage II NSCLC with Zubrod performance status of 0-2

          -  REGISTRATION STEP 1: Participants must not be candidates for surgical resection in the
             opinion of the treating investigator. Participants whose disease was previously
             resected must have experienced local or regional recurrence at least 12 months after
             resection

          -  REGISTRATION STEP 1: Participants must not be candidates for concurrent chemoradiation
             in the opinion of the treating investigator

          -  REGISTRATION STEP 1: Participants must have measurable or non-measurable disease
             documented by computed tomography (CT) or magnetic resonance imaging (MRI). Measurable
             disease must be assessed within 28 days prior to Registration Step 1. Non-measurable
             disease must be assessed within 42 days prior to Step 1 registration. The CT from a
             combined positron emission tomography (PET)/CT may be used only if it is of diagnostic
             quality. All known sites of disease must be assessed and documented on the Baseline
             Tumor Assessment Form (RECIST 1.1)

          -  REGISTRATION STEP 1: Participants must have an MRI or CT scan of the brain with
             contrast within 28 days prior to Registration Step 1

          -  REGISTRATION STEP 1: Participants' disease must fit within the radiation constraints
             in the opinion of a local radiation oncologist

          -  REGISTRATION STEP 1: Participants may have received prior treatment for their lung
             cancer, including surgery, chemotherapy, targeted agents, and/or radiation treatment.
             At least 12 months must have elapsed since last treatment

          -  REGISTRATION STEP 1: Participants may have had prior radiation therapy as long as the
             irradiated area does not overlap with the radiation field targeted for this study

          -  REGISTRATION STEP 1: Participants must have recovered from any adverse effects of
             prior major surgery to the satisfaction of the treating physician. Biopsies and
             central IV access placement are not considered major surgery

          -  REGISTRATION STEP 1: Absolute neutrophil count (ANC) >= 1500/mcl (obtained within 28
             days prior to Registration Step 1)

          -  REGISTRATION STEP 1: Platelet count >= 100,000/mcl (obtained within 28 days prior to
             Registration Step 1)

          -  REGISTRATION STEP 1: Hemoglobin >= 9 grams/dL (obtained within 28 days prior to
             Registration Step 1)

          -  REGISTRATION STEP 1: Total bilirubin =< 1.5 x institutional upper limit of normal
             (IULN) (obtained within 28 days prior to Registration Step 1)

          -  REGISTRATION STEP 1: Aspartate aminotransferase (AST) and alanine aminotransferase
             (ALT) =< 2.5 x IULN (obtained within 28 days prior to Registration Step 1)

          -  REGISTRATION STEP 1: Serum creatinine =< 1.5 x IULN OR measured or calculated
             creatinine clearance >= 40 mL/min (obtained within 28 days prior to Registration Step
             1)

          -  REGISTRATION STEP 1: Participants must have percent predicted diffusing capacity of
             the lungs for carbon monoxide (DLCO) of at least 50% documented within 90 days prior
             to Registration Step 1

          -  REGISTRATION STEP 1: Patient must not have had a prior history of interstitial lung
             disease or > grade 2 (Common Terminology Criteria for Adverse Events [CTCAE] version
             5) pneumonitis

          -  REGISTRATION STEP 1: Participants must not have active autoimmune disease requiring
             therapy within the past 6 months

          -  REGISTRATION STEP 1: Participants must not have an active infection requiring therapy

          -  REGISTRATION STEP 1: Participants must not be pregnant or nursing because atezolizumab
             has not been studied in pregnant or nursing women and the mechanism of action is
             expected to cause fetal harm. Women/men of reproductive potential must have agreed to
             use an effective contraceptive method while on protocol treatment and for five months
             after last dose of atezolizumab. A woman is considered to be of "reproductive
             potential" if she has had menses at any time in the preceding 12 consecutive months.
             In addition to routine contraceptive methods, "effective contraception" also includes
             heterosexual celibacy and surgery intended to prevent pregnancy (or with a side-effect
             of pregnancy prevention) defined as a hysterectomy, bilateral oophorectomy or
             bilateral tubal ligation. However, if at any point a previously celibate patient
             chooses to become heterosexually active during the time period for use of
             contraceptive measures outlined in the protocol, he/she is responsible for beginning
             contraceptive measures

          -  REGISTRATION STEP 1: Participants with known human immunodeficiency virus (HIV)
             infection must be on effective anti-retroviral therapy and must have undetectable
             viral load at their most recent viral load test and within 6 months prior to
             Registration Step 1

          -  REGISTRATION STEP 1: Patient must be tested for hepatitis B within 28 days prior to
             Registration Step 1. Patient must not have active (chronic or acute) hepatitis B virus
             (HBV) infection. Patients may have past or resolved HBV infection. Active HBV is
             defined as having a positive hepatitis B surface antigen (HBsAg) test. Past or
             resolved HBV is defined as having a negative HBsAG test and a positive total hepatitis
             B core antibody (HBcAb) test

          -  REGISTRATION STEP 1: Patients must not have active hepatitis C virus (HCV) infection.
             Active HCV is defined as having a positive HCV antibody test followed by a positive
             HCV ribonucleic acid (RNA) test. Patient must have an HCV antibody test within 28 days
             prior to Registration Step 1. If the HCV antibody test is positive, the patient must
             also have an HCV quantitative RNA test within 28 days prior to Registration Step 1

          -  REGISTRATION STEP 1: No other prior malignancy is allowed except for the following:
             adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer,
             adequately treated Stage I or II cancer from which the patient is currently in
             complete remission, or any other cancer from which the patient has been disease free
             for three years. Participants with localized prostate cancer who are being followed by
             an active surveillance program are also eligible

          -  REGISTRATION STEP 1: Participants must be offered optional participation in banking of
             specimens for future research

          -  REGISTRATION STEP 1: Participants must be informed of the investigational nature of
             this study and must sign and give written informed consent in accordance with
             institutional and federal guidelines

          -  REGISTRATION STEP 1: As a part of the Oncology Patient Enrollment Network (OPEN)
             registration process the treating institution's identity is provided in order to
             ensure that the current (within 365 days) date of institutional review board approval
             for this study has been entered in the system

          -  REGISTRATION STEP 2: Participants must be registered to Step 2 within 42 days after
             completion of radiation treatment. Participants must have received at least 44 Gy of
             radiation treatment

          -  REGISTRATION STEP 2: Participants must have no evidence of progression per RECIST 1.1
             on CT scan of the chest, abdomen, and pelvis performed between 2 and 5 weeks after
             completion of radiation therapy

          -  REGISTRATION STEP 2: Any toxicities from radiation therapy must have resolved to <
             grade 2

          -  REGISTRATION STEP 2: Absolute neutrophil count (ANC) >= 1500/mcl (obtained within 28
             days prior to Registration Step 2)

          -  REGISTRATION STEP 2: Platelet count >= 100,000/mcl (obtained within 28 days prior to
             Registration Step 2)

          -  REGISTRATION STEP 2: Hemoglobin >= 9 grams/dL (obtained within 28 days prior to
             Registration Step 2)

          -  REGISTRATION STEP 2: Total bilirubin =< 1.5 x institutional upper limit of normal
             (IULN) (obtained within 28 days prior to Registration Step 2)

          -  REGISTRATION STEP 2: AST and ALT =< 2.5 x IULN (obtained within 28 days prior to
             Registration Step 2)

          -  REGISTRATION STEP 2: Serum creatinine =< 1.5 x IULN OR measured or calculated
             creatinine clearance >= 40 mL/min (obtained within 28 days prior to Registration Step
             2)

          -  REGISTRATION STEP 2: Participants must not have received steroids in doses of more
             than prednisone 10 mg daily or equivalent within 14 days prior to Registration Step 2

          -  REGISTRATION STEP 2: Participants must not have received a live vaccine within 28 days
             prior to Registration Step 2