Background Adherence to the Surviving Sepsis Campaign's 3- and 6-hour bundles (blood cultures/serum lactate/antibiotics/IV fluids/vasopressors) improves mortality. Septic patients with mental health illness may not receive optimal care, being unable to explain symptoms, understand/accept their condition/care, or remain calm. We compare characteristics of ED septic patients with vs without mental health illnesses in their demographics, insurance, housing status, comorbidities, and infected organs, part of a larger, retrospective study seeking to compare such patients' sepsis care quality (bundle adherence, length-of-stay (LOS)). Methods Patients with sepsis (and their infection source) between 2017-2019 were identified from a health system sepsis reporting database. Their characteristics of history of mental health illness (cognitive, mood, personality, schizophrenia, psychosis, substance use), demographics, insurance, housing status, and comorbidities were obtained via electronic health record query. Such characteristics were compared among patients with vs without mental illness. Results A greater percent of septic patients than the overall U.S. population had a mental illness (26.9% vs 21%). In univariate analysis, patients with mental illnesses were older (77.9 vs 67.6 years), more-likely to be from a psychiatric facility/group home (32.5% vs 2.1%; p<0.0001), have Medicare (58% vs 47.1%; p=0.0201), have more than 1 comorbidity (72.6% vs 0.6%; p<0.0001), and have a respiratory source of sepsis. People without mental illnesses were more-often from either a private home/nursing home (75.2% vs 56.7%; p<0.0001) or clinic (8.9% vs 3.2%; p=0.0191), have private insurance (15.2% vs 7.6%; p=0.0167), and have immune- modifying medications or cancer (20.7% vs 7%; p<0.0001). Discussion Compared with national rates of mental health illness, a higher percent of septic patients (26.9% vs. 21%) had mental illness (mostly neurocognitive). Septic patients with mental illnesses tended to be older, from a psychiatric facility/group home, have Medicare, have ≥1 comorbidity, and have a respiratory source of sepsis. Patients without mental illnesses more-often had immune-modifying medications and malignancy. Patients with mental health illnesses were more-likely to have a respiratory source of their sepsis, perhaps due to higher risk for aspiration or respiratory contagion in group homes/psychiatric facilities. Clinicians may want to specifically test or empirically treat for respiratory sources in this population. Future analyses (multivariate) will determine whether differences in quality of care, mortality, or length of stay exist, and if specific characteristics above were associated with these different outcomes. Limitations: The study was based on data from a single hospital system, which might limit generalizability. Additionally, the study relied on data collected for sepsis management, which might not capture all patients with sepsis or those who did not receive the sepsis bundle. Furthermore, all data collected pertaining to this study was only in the timeframe between 2018-2019. The proportion of septic patients with vs. without mental health disorders during and following the COVID pandemic may differ from the earlier time frame represented in this study.