At least 10% of lung cancers arise in adults who have never smoked. Data remain inconclusive on whether lung cancer incidence has been increasing among never-smoking adults. How have age-adjusted incidence rates of lung cancer changed temporally, especially among never-smoking adults? Trends in lung cancer incidence were examined using linked electronic health record and cancer registry data on a dynamic cohort of adults aged ≥30 years at risk for incident lung cancer between 1/1/2007 and 12/31/2018 from an integrated healthcare system in northern California. Truncated age-adjusted lung cancer incidence rates and average annual percentage change (AAPC) in rates were estimated, overall and separately for ever- and never-smoking adults by age, sex, and race/ethnicity. Our cohort included 3,751,348 (52.5% female; 48.0% non-Hispanic White; 63.1% never-smoking) adults, among whom 18,627 (52.7% female; 68.6% non-Hispanic White; 15.4% never-smoking) were diagnosed with lung cancer. The overall lung cancer incidence rate declined from 91.1 to 63.7 per 100,000 person-years between 2007-2009 and 2016-2018 (AAPC, -3.9%; 95% CI, -4.2%, -3.6%). Among ever-smoking adults, incidence rates declined overall from 167.0 to 113.4 per 100,000 person-years (AAPC, -4.2%; 95% CI, -4.4%, -3.9%) and, to varying degrees, within all age, sex, and racial/ethnic groups. Among never-smoking adults, incidence rates were relatively constant, with three-year period estimates ranging from 19.9 to 22.6 per 100,000 person-years (AAPC, 0.9%; 95% CI, -0.3%, 2.1%). Incidence rates for never-smoking adults appeared stable over time within age, sex, and racial/ethnic groups, except for those of Asian and Pacific Islander (API) origin (AAPC, 2.0%; 95% CI, 0.1%, 3.9%), whose rates were about twice as high compared to their counterparts. These observed trends underscore the need to further elucidate the etiology of lung cancer in never-smoking adults, including why incidence is higher and rising in never-smoking API adults.