BACKGROUND: Public health programs varied in ability to reach people with COVID-19 and their contacts to encourage separation from others. For both adult cases of COVID-19 and contacts, we estimated the impact of contact tracing activities on separation behaviors from January, 2020 until March, 2022. METHODS: We used a probability-based panel survey of a nationally representative sample to gather data for estimates and comparisons. RESULTS: An estimated 64,255,351 adults reported a positive SARS-CoV-2 test result; 79.6% isolated for >5 days, 60.2% isolated for >10 days, and 79.2% self-notified contacts. 24,057,139 (37.7%) completed a case investigation and 46.2% reported contacts to health officials. More adults who completed a case investigation isolated than adults who did not (>5 days, 82.6%; >10 days, 69.8% versus >5 days, 78.2% and >10 days 54.8%; p-values for both measures <0.05).84,946,636 adults were a contact to a COVID-19 case; 73.1% learned of their exposure directly from a case; 49.4% quarantined for >5 days, 18.7% quarantined for >14 days, and 13.5% completed a contact tracing call. More who completed a contact tracing call quarantined than those who did not (>5 days, 61.2%; >14 days, 25.2% versus >5 days, 48.5%; >14 days, 18.0%; p-values for both measures <0.05). CONCLUSIONS: Engagement in contact tracing positively correlated with isolation and quarantine. However, most adults with COVID-19 isolated and self-notified contacts regardless of whether the public health workforce was able to reach them. Identifying and reaching contacts was challenging, and limited the ability to promote quarantining, and testing.