Objectives. To characterize severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mitigation strategies, testing, and cases across county jails in the Southeastern United States, examining variability by jail characteristics. Methods. We administered a 1-time telephone survey to personnel of 254 jails in Alabama, Georgia, North Carolina, and South Carolina between October 2020 and May 2021. Results. Some SARS-CoV-2 mitigation strategies (e.g., screening at intake, isolation and masking for symptomatic persons) were commonly reported (≥ 75% of jails). Other measures, such as masking regardless of symptoms (52%) and screening at release (26%), were less common and varied by jail state or population size. Overall, 41% of jails reported no SARS-CoV-2 testing in the past 30 days. Jails with testing (59%) tested a median of 6 per 100 incarcerated persons; of those jails, one third reported 1 or more cases of positive tests. Although most jails detected no cases, in the 20% of all jails with 1 or more case in the past 30 days, 1 in 5 tests was positive. Conclusions. There was low testing coverage and variable implementation of SARS-CoV-2 mitigation strategies in Southeastern US jails during the first year of the COVID-19 pandemic. (Am J Public Health. 2022;112(11):1589-1598. https://doi.org/10.2105/AJPH.2022.307012).