National Stepfamily Day is celebrated annually on September 16 and was founded by stepparent Christy Tusing-Borgeld in 1997. The 2000 Census was the first decennial census to collect information on the type of relationship between householders and their children, whether biological, step or adoptive. The same answer categories were introduced to the American Community Survey in 2008. Beginning in 2007, the Current Population Survey asked respondents to identify both a co-resident mother and father, as well as the type of relationship between the child and their parents.
Source: 2019 American Community Survey (ACS) 1-Year Estimates.
Note: Table B09018 above is transposed and cropped on the right to highlight the United States. Click on the image for the full table.
From Census.gov > Topics > Families and Living Arrangements:
From the Newsroom > Stats for Stories (SFS):