Background Mississippi has among the highest prevalence of sexually transmitted infections (STIs) in the United States. Understanding sexual networks can provide insight into risk factors for transmission and guide prevention interventions. Methods Participants included 1437 primarily African American (95%) adults presenting for care at an STI clinic in Jackson, Mississippi. Latent class analysis identified underlying population subgroups with unique patterns of response on a comprehensive set of 14 sexual partner variables, such as living with or having a child with a partner, partner dependence and trust, 1-time sexual encounters, multiple main partners, substance use, sexual concurrency, and incarceration. Classes were compared on participant age, sex, sexual orientation, public assistance, lifetime partners, relationship status, and self-reported past-year STI. Results Three classes emerged. Class 1 (n = 746) participants were less dependent on partners and less likely to live with or have a child with a partner. Class 2 participants (n = 427) endorsed multiple STI risk factors, including partner incarceration, 6 or more lifetime partners, sexual concurrency, 1-time sexual encounters, and substance use at last sex. Class 3 participants (n = 226) were more likely to be in dependent, committed relationships with children. Class 2 had a higher proportion of self-report past-year STIs (36.7%) compared with classes 1 (26.6%) and 3 (26.1%). Conclusions Certain partner factors such as incarceration, substance use, and concurrency may contribute to increased STI risk. Partner factors may be useful proxies for STI risks and could be useful questions to include in screening questionnaires in clinical settings.