Racially mixed children are a rapidly expanding segment of American families, signaling the ongoing blurring of racial boundaries. Most of what is known about multiraciality is drawn from analyses of two-parent families even as marriage became decreasingly tied to childbearing. The current study tracked the prevalence and racial composition of multiracial families where parents are married and unmarried from 1980 until 2018 using data from the U.S. Census and American Community Survey. We find that multiracial families are increasingly common amongst married and unmarried parents with the greatest growth occurring among White unmarried mothers, nearly 15% of whom have multiracial children as of 2018. Additionally, we find that Asian-White and Hispanic-White children are more likely to live in married families while Black-White and dual minority children are disproportionately represented amongst single-parent families. Ultimately, capturing the complexity of racialized contexts where multiracial children are found, as well as how the prevalence of these contexts has changed over time, requires accounting for family structure differences.