Study Objective: Among a comprehensive range of frontline emergency department health care personnel, we assessed symptoms of anxiety and burnout, specific coronavirus disease 2019 (COVID-19) work-related stressors, and risk for post-traumatic stress disorder (PTSD). We also determined whether COVID-19 serologic testing of HCP decreased their self-reported anxiety. Methods: In a prospective cohort study from May 13, 2020, to July 8, 2020, we used electronic surveys to capture participant self-reported symptoms before and after serologic testing for anti-SARS-CoV-2 immunoglobulin G antibodies. Participants were physicians, nurses, advanced practice providers, and nonclinical ED personnel at 20 geographically diverse United States EDs. We evaluated these domains: 1) the effects of the COVID-19 pandemic on overall stress and anxiety; 2) COVID-19-related work stressors; 3) burnout; and 4) PTSD risk (measured using the Primary Care-PTSD Screen for DSM-5, a 5-item screening instrument in which a score of ≥3 signifies high risk for PTSD). We also assessed perceptions of whether results of COVID-19 antibody testing decreased participants’ self-reported anxiety. Results: Of 1,606 participants, 100% and 88% responded to the baseline and follow-up surveys, respectively. At baseline, approximately half (46%) reported symptoms of emotional exhaustion and burnout from their work, and 308 (19.2%, 95% confidence interval [CI] 17.3% to 21.1%) respondents screened positive for increased PTSD risk. Female respondents were more likely than males to screen positive (odds ratio [OR] 2.03, 95% CI 1.49 to 2.78). Common concerns included exposing their family and the health of coworkers diagnosed with COVID-19. After receiving antibody test results, 54% (95% CI 51.8 to 56.7) somewhat agreed, agreed, or strongly agreed that knowledge of their immune status had decreased their anxiety. A positive serology result indicating prior SARS-CoV-2 infection was associated with a higher likelihood of reporting decreased anxiety (2.83, 95% CI 1.37 to 5.83). Conclusion: Symptoms of anxiety and burnout were prevalent across the spectrum of ED staff during the COVID-19 pandemic. One-fifth of ED personnel appeared to be at risk for PTSD. Increased provision of serologic testing may help to mitigate anxiety.