Poor pulmonary function (PPF) is associated with increased risk of dementia, yet it is unclear if PPF in early adulthood to midlife increases risk, independent of smoking and subsequent vascular disease. This study evaluated the association between multiple markers of PPF in early adulthood to midlife and long-term risk of dementia. We evaluated 27,387 members of an integrated health care system with forced expiratory volume in 1, 2 seconds, and vital capacity collected from 1964 to 1973 (mean age=41.8±4.2 y). Associations of PPF with dementia diagnoses from January 1, 1996 to September 30, 2015 were evaluated with Cox proportional hazards models adjusted for demographics, height, body mass index, hypertension, smoking status, diabetes, stroke, and heart failure. In total, 7519 individuals (27%) were diagnosed with dementia. In fully adjusted Cox proportional hazards models, for all PPF measures each liter decrease was associated with a 13% to 14% higher risk of dementia. Compared with the highest quintile, the first quintile of PPF measures were associated with a 24% to 28% increased risk of dementia; second to fourth quintiles showed strong dose-dependent associations. Results were similar when stratified by smoking status. In this large, diverse cohort, multiple measures of PPF in early adulthood to midlife were associated with dementia risk independent of smoking and vascular comorbidities.