Purpose Research on urban/rural disparities in alcohol, drug use, and mental health (ADM) conditions is inconsistent. This study describes ADM condition prevalence and access to care across diverse geographies in a predominantly rural state. Methods Multimodal cross‐sectional survey in South Dakota from November 2013 to October 2014, with oversampling in rural areas and American Indian reservations. Measures assessed demographic characteristics, ADM condition prevalence using clinical screenings and participant self‐report, perceived need for treatment, health service usage, and barriers to obtaining care. We tested for differences among urban, rural, isolated, and reservation geographic areas, controlling for participant age and gender. Findings We analyzed 7,675 surveys (48% response rate). Generally, ADM condition prevalence rates were not significantly different across geographies. However, respondents in isolated and reservation areas were significantly less likely to have access to primary care. Knowledge of treatment options was significantly lower in isolated regions and individuals in reservation areas had significantly lower odds of reporting receipt of all needed care. Across the sample there was substantial discordance between ADM clinical screenings and participant self‐reported need; 98.1% of respondents who screened positive for alcohol or drug misuse and 63.8% of respondents who screened positive for a mental health condition did not perceive a need for care. Conclusion In a predominantly rural state, geographic disparities in ADM conditions are related to differences in access as opposed to prevalence, particularly for individuals in isolated and reservation areas. Educational interventions about ADM condition characteristics may be as important as improving access to care.