Immune checkpoint inhibitors (ICIs) greatly improved outcomes of stageIV non-small cell lung cancer (NSCLC) in randomized clinical trials. Limited data exists regarding the survival improvement of ICI use at the population level. Clinical data of patients with pathologically confirmed stageIV NSCLC diagnosed in 2013 and 2017 were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. Survival outcomes were compared before and after ICI use to assess the survival improvement in the immunotherapy era in the real world. A total of 19,433 patients with stageIV NSCLC were included. Being female, age < 60years, of American Indian and Asian or Pacific Islander race, married, non-squamous histology, without bone, brain, or liver metastases, and receiving chemotherapy were significantly associated with better prognosis in multivariable analyses. Propensity score matching (PSM) based on associated factors resulted in 8743 patients each in the non-immunotherapy and immunotherapy groups (1:1 ratio). After PSM, both overall survival (OS) (p < 0.001) and cancer-specific survival (CSS) (p < 0.001) were significantly improved in the immunotherapy group. The median OS (mOS) was 6.0months in the non-immunotherapy group and 8.0months in the immunotherapy group. The 1-, 2-, and 3-year OS rate was 29.0%, 14.2%, and 8.5% in the non-immunotherapy group, and 37.8%, 23.5%, and 16.7% in the immunotherapy group, respectively. Patients who were male, under 60years old, married, white, had adenocarcinoma, had no bone or liver metastases, and received chemotherapy or radiation therapy were more likely to benefit from immunotherapy. Survival outcomes of patients with stageIV NSCLC were significantly improved in the immunotherapy era. Population-level benefits of survival varied among subgroups, and not all the increase in OS meant a clinically meaningful benefit.