The role of parks and nature to support well-being during the COVID-19 pandemic is uncertain. To examine this topic, we used mixed-methods data collected in April-May 2020 from US adults aged ≥55 in the COVID-19 Coping Study. We quantitatively evaluated the associations between number of neighborhood parks and depression, anxiety, and loneliness; and conducted qualitative thematic analysis of participants' outdoor experiences. Among urban residents, depression and anxiety were inversely associated with the number of neighborhood parks. Thematic analysis identified diverse engagement in greenspaces that boosted physical, mental, and social well-being. The therapeutic potential of outdoor and greenspaces should be considered for interventions during future epidemics.