BACKGROUND: Earlier and more severe onset of chronic health conditions contributes to the increased risk of premature death among adults experiencing homelessness. Trimorbidity, a subset of multimorbidity representing overlap of physical health, mental health, and substance use conditions, disproportionately impacts adults experiencing homelessness. We know of no longitudinal data comparing trimorbidity trends among adults experiencing homelessness. OBJECTIVE: To characterize 19-year trimorbidity trends among adults experiencing homelessness. RESEARCH DESIGN: Repeated longitudinal, statewide survey administered every 3 years. SUBJECTS: Adults living throughout Minnesota experiencing homelessness. MEASURES: Reported diagnoses of chronic health conditions within 3 categories: physical health conditions (hypertension, heart disease, asthma, diabetes); mental health conditions (depression, posttraumatic stress disorder, bipolar disorder, schizophrenia/other paranoid, and delusional disorders); and substance use conditions (alcohol and illicit substances). RESULTS: A total of 25,552 surveys were completed by adults at 3-year intervals in a total of 7 waves. Participants reported increasing frequency and duration of homelessness, and more nights slept outside/in a car. 77.3% of adults experiencing homelessness in 2018 had one or more chronic health condition in any domain. From 2000 to 2018, bimorbidity and trimorbidity surpassed morbidity within a single domain. This was driven by increases in mental health conditions. In 2018, 31.7% of participants reported bimorbidity and 16.3% of adults reported trimorbidity. CONCLUSIONS: Adults experiencing homelessness bear a substantial and growing burden of bimorbidity and trimorbidity. Ensuring accessible, high quality care that includes robust services that can address all 3 categories of health is critical. Such care is best delivered in combination with affordable supportive housing.