Introduction The current framework for investigating respiratory diseases is based on defining lung health as the absence of lung disease. In order to develop a comprehensive approach to prevent the development of lung disease, there is a need to evaluate the full spectrum of lung health spanning from ideal to impaired lung health. The American Lung Association (ALA) Lung Health Cohort is a new, population-based, cohort study focused primarily on characterising lung health in members of the millennial generation without diagnosed severe respiratory disease. Participants will be enrolled for the baseline study visit starting in 2021, and funding will be sought to support future study exams as part of a longitudinal cohort study. This study will be crucial for developing a novel paradigm of lung health throughout the adult life course. Methods and analysis This study will leverage the existing infrastructure of the ALA Airways Clinical Research Centers network to enrol 4000 participants between ages 25 and 35 years old at 39 sites across the USA between April 2021 and December 2024. Study procedures will include physical assessment, spirometry, chest CT scan, accelerometry and collection of nasal epithelial lining fluid, nasal epithelial cells, blood and urine. Participants will complete questionnaires about their sociodemographic characteristics, home address histories and exposures, work history and exposure, medical histories, lung health and health behaviours and activity. Ethics and dissemination The study was approved by the Johns Hopkins Medicine Institutional Review Board. Findings will be disseminated to the scientific community through peer-reviewed journals and at professional conferences. The lay public will receive scientific findings directly through the ALA infrastructure including the official public website. Deidentified datasets will be deposited to BioLINCC, and deidentified biospecimens may be made available to qualified investigators along with a limited-use datasets.