Jails are optimal settings in which to screen individuals for opioid use disorders (OUD) and provide needed services, especially medications for OUD (MOUD). This study sought to assess the availability of OUD “best practices” in jails located in counties heavily impacted by opioid overdose in the U.S. and their related training and resource needs. Counties were selected for study inclusion using two indicators of OUD severity: the absolute number and population rate of opioid overdose deaths. Structured interviews were completed with representatives from 185/244 (76%) of targeted counties and 185/250 (74%) of targeted jails in these counties. Ten OUD best practices were identified based on current treatment and practice guidelines. These include: screening for OUD; clinical assessment; medically managed withdrawal; MOUD administration; MOUD for pregnant people; counseling and wrap-around services; collaboration with community providers; assistance with Medicaid/insurance; re-entry services; and overdose prevention. Descriptive analyses examined the provision of any services and average percentage of services endorsed within best-practice categories, association of best-practice availability with community and jail characteristics, and related needs for training and resources.