In the first 6 months of the coronavirus disease 2019 pandemic, limited testing clouded understanding of the extent of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission in Africa. In particular, Tanzania halted all testing and reporting of SARS-CoV-2 cases after May 2020, not resuming until June 2021. In July-August 2020, we performed a seroprevalence survey in rural Bagamoyo district, 40 km outside Dar es Salaam. Among 347 asymptomatic children and adults, 64/347 (18.0%) demonstrated seroreactivity to SARS-CoV-2 spike receptor binding domain by ELISA. Given significant antibody cross-reactivity in malaria-endemic regions, seropositivity was additionally confirmed via a multitarget Luminex immunoassay. Thirty-seven, or 58% of initially seroreactive persons, were Luminex positive, leading to an estimated SARS-CoV-2 seroprevalence of 10.7% (37/347, 95% CI 7.6-14.4%). Working in health care appeared to be associated with seropositivity. Reporting of viral symptoms or health care-seeking behavior in the previous 3 months was not more frequent in seropositive individuals.