Initial reports suggest that mental health problems were elevated early in the COVID-19 pandemic. However, few studies have followed-up participants as the pandemic evolved and examined both between and within person predictors of symptom trajectories. In the current study, adolescents and young adults (N=532) in New York were surveyed monthly between March 27 and July 14, 2020, a period spanning the first peak and subsequent decline in COVID-19 infection rates in the region. Surveys assessed symptoms of depression and anxiety using the Child Depression Inventory and the Screen for Child Anxiety Related Disorders, as well as experiences related to the pandemic. Multilevel growth modeling indicated that symptoms of depression and anxiety peaked around late April/early May and then decreased through May-July. Some pandemic experiences followed a similar quadratic trajectory, while others decreased linearly across the study. Specific relationships emerged between some types of pandemic experiences and depression and anxiety symptoms. While symptoms of depression and anxiety in youth may have been elevated early in the pandemic, these findings suggest they subsided across Spring-Summer of 2020, with higher levels of both corresponding to a period of peak infection rates and decreases paralleling the decline in pandemic experiences and COVID-19 infection rates.