Background: Data are limited regarding the prevalence of substance use among adolescents in rural and ethnically diverse communities. This study examined rates and sociodemographic correlates of lifetime substance use among adolescents in Mississippi, a rural state that is the poorest in the country (21.3% poverty rate) and has the largest proportion of African Americans per capita (36.3%). Methods: Participants in this cross-sectional study were 6349 adolescents (6th through 12th grade) who reported on lifetime tobacco, alcohol, marijuana, cocaine, inhalant, hallucinogen, and methamphetamine use. Results: Lifetime smoking (10.2% to 44.5%), alcohol (23.2% to 72.0%), and marijuana use (7.9% to 39.2%) increased steadily when comparing students in 6th to 12th grade. Substances with more serious abuse potential (cocaine [6.7% to 11.1%], inhalants [12.2% to 17.9%], hallucinogens [4.4% to 12.1%], and methamphetamine [3.0% to 6.7%]) displayed more modest increases across grade. Adolescents who classified their race/ethnicity as "Other" (i.e., not white, black/African American, Asian, or Hispanic/Latino/Latina) demonstrated more than 2-fold increased likelihood of methamphetamine use (odds ratio [OR] = 2.42), and increased risk for use of any illicit substance (OR = 1.49). In general, males demonstrated an increased risk for use across substances (OR = 1.15--1.94), and higher income was associated with a decreased likelihood of illicit substance use (OR = 0.51--0.67). Living in a more populated area was associated with an increased likelihood of alcohol (OR = 1.43), marijuana (OR = 2.11), and cocaine use (OR = 2.06), and use of any illicit substance (OR = 1.54). Conclusions: Mississippi adolescents reported higher rates of lifetime cocaine, inhalant, hallucinogen, and methamphetamine use across all grade levels compared with national surveys. Male gender, low income, and residence in more populated areas were associated with increased use of several substances. Findings demonstrate the need for prevention and intervention programs targeting impoverished rural and ethnically diverse communities.