Background <p>The COVID-19 pandemic has been shown to worsen mental health outcomes, particularly among minority youths. However, few studies have examined whether neighborhood composition—specifically greater co-ethnic density, which has been linked to better mental health in other contexts—might buffer against these negative effects. Furthermore, existing studies linking neighborhood ethnic composition to health tend to be based in the U.S., where racial/ethnic clustering is intrinsically intertwined with racial discrimination, making it hard to unpack the impact of neighborhood composition on mental health. This study examines how neighborhood composition, as estimated by a spatial measure of neighborhood-scale residential segregation, relates to mental health outcomes of youths of different ethnicities before and during the COVID19 pandemic, in Singapore, a multi-ethnic city-state with a large Chinese majority and long-standing policies to ensure sociospatial ethnic mix within neighborhoods.</p> Methods <p>Four waves of survey responses of over 3000 youths were collected between 2019 and 2022, and joined to estimates of their neighborhood characteristics, include residential ethnic and socioeconomic segregation, built density and average housing prices. First, multi-level models were fitted, where individual observations were nested within individual participants. Random intercepts were fitted for each participant to account for unobserved individual-specific effects, while three-way interactions between the fixed effects of individual’s ethnicity, neighborhood-level co-ethnic density/residential segregation estimates and survey wave were included as a test of whether the observed associations varied by ethnicity and time. The second approach modelled ‘typical’ mental health trajectories across the survey waves using latent class growth analysis. Multinomial logistic regression predicting latent class membership with covariates were then fitted to analyse whether and how youths’ ethnic identities and residential co-ethnic density/ segregation exposure related to different mental health trajectories.</p> Results <p>Ethnic minority youths living in areas with lower levels of ethnic residential segregation, which in Singapore is characterised by greater co-ethnic density, had better mental health outcomes over the course of the pandemic, compared to peers living in more homogenously Chinese neighborhoods. Results from the multi-level models however suggest this ‘protective’ relationship of experiencing greater co-ethnic density dissipated during the height of the COVID-19 pandemic in 2020.</p> Conclusions <p>Living in areas with higher co-ethnic density for minority groups, and a lower spatial concentration of residents of majority ethnicity, might be protective of minority youths’ mental health. However, this protective effect of greater residential ethnic mix might be contingent on there being in-person interactions, which were severely reduced during the height of a pandemic. This finding thus underscores the need for initiatives to maintain social connectedness within one’s neighborhood even in the face of safe distancing measures.</p>