We documented changes in depressive and anxiety symptoms from before to during the COVID-19 pandemic among young adults and investigated whether changes differed across participant characteristics. Data were available in an investigation of 1294 grade 7 students recruited in 1999–2000. For this analysis, we used data collected pre-pandemically in 2017–20 (mean (SD) age = 30.6 (1.0)) and during the pandemic in 2020–21 (mean (SD) age = 33.6 (0.6)). 673 participants with data in both cycles were retained for analysis. Symptoms were measured using the Major Depression Inventory (MDI) and the Generalized Anxiety Disorder-7 (GAD-7) scale. Standardized mean differences (SMD) of changes in MDI and GAD-7 values between cycles were calculated across participant characteristics. On average, MDI scores increased by 2.1 (95%CI 1.4, 2.8) points during the pandemic from mean 10.5; GAD-7 scores increased by 1.2 (0.8, 1.5) points from mean 4.7. The SMD was 0.24 (0.14, 0.33) for MDI, and 0.24 (0.13, 0.34) for GAD-7. No differences in MDI change scores were observed across participant characteristics. Differences in GAD-7 change scores were observed by mood/anxiety disorder (SMD − 0.31 (− 0.58, − 0.05)), household income (0.24 (0.02, 48)), living with young children (− 0.56 (− 1.23,− 0.05)), and adherence to public health recommendations 0.58 (0.19, 1.03)). Increases in depressive and anxiety symptoms were observed 10–16 months into the COVID-19 pandemic among adults age 32–36.