Background: The United States operates roughly 6,300 correctional facilities, clustered around environmental hazards, with new facility construction ongoing. While research has shown the health harms associated with high incarceration rates, less is known about the health of communities living near prisons and jails.

Methods: We conducted a cross-sectional ecological analysis at the census tract level to examine the association between residential proximity to jails or prisons and asthma emergency department (ED) visit rates in California. We generated buffers of varying distance thresholds around facilities (0.25, 0.5, and 1 mile for jails; 1, 2, and 5 miles for prisons) and classified tracts overlapping a buffer as proximate. Multivariable linear models assessed the tract-level association between jail or prison proximity and asthma ED visits, adjusting for urbanicity, percent Black, unemployment rate, median household income, percent uninsured, primary care provider shortage, ozone concentration, and particulate matter (PM)2.5.

Findings: At the 1-mile threshold, 655 census tracts (8.2%) with over 3 million residents were classified as proximate to a jail, while 543 tracts (6.8%) were proximate to a prison. Jail proximity was significantly positively associated with asthma ED visit rates after controlling for covariates across all distance thresholds tested. Effects did not monotonically decrease with increasing distance (0.25-mile: β=3.6; 0.5-mile: β=5.6; 1-mile: β=4.5). Prison proximity was not significantly associated with asthma ED visit rates at any distance threshold.

Conclusions: California census tracts proximate to jails experience a greater burden of asthma ED visits than explained by measured socioeconomic and environmental covariates. While causality remains unclear, the findings suggest potential health risks associated with jail proximity, with implications for the health of incarcerated individuals, staff, and surrounding communities.