Social support is a critical factor for women’s engagement with substance use treatment and recovery, particularly for women with criminal-legal system involvement. However, less is known about the social support networks of incarcerated women, particularly as a function of service engagement. Thus, this paper aims to describe the structure, composition, and function of social support networks of women with opioid use disorder (OUD) incarcerated in jails; and compare network differences between women receiving jail-based substance use treatment and non-treatment participants.