Background: We sought to examine racial and ethnic disparities in test positivity rate and mortality among emergency department (ED) patients tested for COVID-19 within an integrated public health system in Northern California. Methods: In this retrospective study we analyzed data from patients seen at three EDs and tested for COVID-19 between April 6 through May 4, 2020. The primary outcome was the test positivity rate by race and ethnicity, and the secondary outcome was 30 day in-hospital mortality. We used multivariable logistic regression to examine associations with COVID-19 test positivity. Results: There were 526 patients tested for COVID-19, of whom 95 (18.1%) tested positive. The mean age of patients tested was 54.2 years, 54.7% were male, and 76.1% had at least one medical comorbidity. Black patients accounted for 40.7% of those tested but 16.8% of the positive tests, and Latinx patients accounted for 26.4% of those tested but 58.9% of the positive tests. The test positivity rate among Latinx patients was 40.3% (56/139) compared with 10.1% (39/387) among non-Latinx patients (p < 0.001). Latinx ethnicity was associated with COVID-19 test positivity (adjusted odds ratio 9.6, 95% confidence interval: 3.5-26.0). Mortality among Black patients was higher than non-Black patients (18.7% vs 1.3%, p < 0.001). Conclusion:We report a significant disparity in COVID-19 adjusted test positivity rate and crude mortality rate among Latinx and Black patients, respectively. Results from ED-based testing can identify racial and ethnic disparities in COVID-19 testing, test positivity rates, and mortality associated with COVID-19 infection and can be used by health departments to inform policy.