Among the 350 largest counties in the US, the median rate of low birth weight was 8.1 percent in 2018. The median rate of low birth weight was 13.5 percent among births to Black mothers, which is more than twice the median rate among births to white mothers. More diverse neighborhoods and higher household income are associated with a lower rate of low birth weight among Black mothers. To reduce racial disparities in low birth weight, policymakers should foster opportunity-rich and inclusive neighborhoods.