Ethnic proportions of neighborhoods are a "macro" measure of intergroup contact and can buffer or expose people of color to discrimination. Simultaneously, perceived discrimination can sensitize students of color to social identity threat in environments in which they are numerically underrepresented and negatively stereotyped. In the current research, we integrate these two lines of research to examine whether neighborhood ethnic composition - the percentage of Latinx residents in one's home community - predicts social identity threat for Latinx students attending college at a predominately White institution (PWI). In two studies, Latinx college students attending a PWI provided their 5-digit zip code and completed measures assessing their perceived discrimination and social identity threat. Across both studies, neighborhood ethnic composition (greater percentage of Latinx residents) was associated with greater social identity threat and this association was mediated by greater perceived discrimination. These studies advance research on neighborhood ethnic composition and social identity threat.