<p>Trajectories of age-related neurocognitive decline are nonuniform, and are impacted by numerous environmental and physiological factors. Earlier life phases set the stage for later life neurocognitive function, with midlife marking a critical transition characterized by increasing variability in cognitive, affective, and physiological functioning. Despite its importance, this turbulent period remains underrepresented in open neuroimaging data resources. To address this gap, the Nathan Kline Institute - Rockland Sample (NKI-RS) created ‘Mapping Interindividual Variation in the Aging Connectome’ (MIVAC), an openly shared, multimodal dataset designed to map brain aging trajectories beginning in midlife and assess the influence of key modifiable factors linked to dementia prevention such as cardiorespiratory fitness, sleep, and mood. This longitudinal investigation includes 348 community-ascertained participants aged 38 to 71 years at baseline, with 219 participants completing 3 annual timepoints. Data collection incorporated deep phenotyping, including detailed assessment of cognitive, behavioral, medical, and cardiorespiratory fitness domains, to compliment multimodal neuroimaging (resting-state fMRI, diffusion MRI, morphometric MRI, and arterial spin labeling) and biospecimen collection. The protocol harmonizes with prior NKI-RS sub studies, enabling lifespan cross-sectional or longitudinal questions, while incorporating age-specific considerations for cognitive and neural aging. The full dataset is openly available.</p>