We study the social construction of race boundaries by investigating patterns in the race, ancestry, and Mexican origin responses provided for children of 14 types of interracial marriages using dense restricted-use data from 1970 to 2010. Our broader purpose is to expose social processes that convert a newborn child of mixed heritage into an adult person of a particular race. We include a more diverse set of families, a longer time span, and more accurate estimates than prior research. These expansions bear fruit.Taking ancestry responses into account and studying the longer-term patterns reveals that mixed-heritage responses have been common since 1980. Expanding the types of mixed heritage and including double-minorities shows that there is substantial variation in response patterns across the 14 groups.