Background <p>Recognizing the disparate health status of correctional populations compared to the general population, national agencies have called for research to better understand disease epidemiology and healthcare needs of individuals in jails. This paper introduces the Registry of Electronic Archives in Correctional Healthcare (REACH) database – a largescale, multivariable living database derived from electronic healthcare records (EHR) of individuals discharged from jails across the nation beginning in 2013. We describe methods used to secure data, detail current database contents, and offer an initial presentation of sample demography. To demonstrate REACH’s utility, an investigation of factors contributing to length of stay (LOS), including demography, health status, and jail characteristics, was conducted.</p> Results <p>The current REACH sample (<i>N</i> = 1,251,837) is primarily comprised of males (72.0%) identified racially as White (55.3%) in their mid-30’s. While detained, approximately 20% and 17% of individuals were prescribed treatment for chronic medical and/or mental health conditions, respectively. Multilevel modeling was used to examine if sex, race, health condition, and/or jail location or size predicted LOS.</p> Conclusions <p>By accessing EHR data, we can expand our understanding of assessment and treatment of specific healthcare conditions in jail populations and address complicated questions about health status of detainees. Data analysis using the REACH database suggests LOS is influenced slightly by jail characteristics and more substantively by detainee demography and medical/mental health conditions. We propose the REACH database’s potential for answering important questions about health status and healthcare services for jail populations, including questions about epidemiology and correctional healthcare.</p>