Objectives: During June–July 2021, an outbreak of SARS-CoV-2 occurred among attendees of a summer youth camp in Nebraska. We assessed the factors that contributed to onward transmission of disease. Methods: The Four Corners Health Department conducted an outbreak investigation and recorded both laboratory-confirmed and self-reported cases of SARS-CoV-2 and mitigation measures employed. We generated sequences on positive specimens, created an epidemic curve to assist with outbreak visualization, and examined epidemiologic, genomic, and laboratory outcomes. Results: Evaluation of 3 index cases led to the identification of 25 people with COVID-19 who interacted directly with the camp. Contact tracing revealed an additional 18 cases consistent with onward community transmission. Most (24 of 35, 68.5%) vaccine-eligible community cases were not vaccinated. We sequenced 8 positive specimens; all were identified as the Delta variant. Precamp planning incorporated local health officials who recommended wearing face masks, practicing social distancing, and using attendee cohorts to limit mixing of people involved in various activities. Conclusion: Low vaccination levels and poor face mask–wearing habits among attendees resulted in secondary and tertiary spread of SARS-CoV-2 and severe outcomes among young adults. This outbreak of COVID-19 at a youth camp highlights the importance of vaccination and use of other measures to interrupt opportunities for SARS-CoV-2 spread in the community and shows that vaccinated people remain vulnerable to infection when in an environment of high exposure to SARS-CoV-2. Proactive case identification and interruption of chains of transmission can help decrease the number of cases and avoid further severe outcomes.