question: BACKGROUND: Outbreaks of COVID-19 have been reported in nursing homes and assisted living facilities; however, the extent of asymptomatic and pre-symptomatic SARS-CoV-2 infection in this high-risk population remains unclear. METHODS: We conducted an investigation of the first known outbreak of SARS-CoV-2 at a skilled nursing facility (SNF) in Illinois on March 15, 2020 and followed residents for 30 days. We tested 126/127 residents for SARS-CoV-2 via RT-PCR and performed symptom assessments. We calculated the point prevalence of SARS-CoV-2 and assessed symptom onset over 30-day follow-up to determine: 1) the proportion of cases who were symptomatic, pre-symptomatic, and asymptomatic and 2) incidence of symptoms among those who tested negative. We used the Kaplan-Meier method to determine the 30-day probability of death for cases. RESULTS: Of 126 residents tested, 33 had confirmed SARS-CoV-2 on March 15. Nineteen (58%) had symptoms at the time of testing, 1 (3%) developed symptoms over follow-up, and 13 (39%) remained asymptomatic. Thirty-five residents who tested negative on March 15 developed symptoms over follow-up; of these, 3 were re-tested and 2 were positive. The 30-day probability of death among cases was 29%. CONCLUSIONS: SNFs are particularly vulnerable to SARS-CoV-2, and residents are at risk of severe outcomes. Attention must be paid to preventing outbreaks in these and other congregate care settings. Widespread testing and infection control are key to help prevent COVID-19 morbidity and mortality in these high-risk populations.