Here are the couple of other things I wanted to point out. Here are the numbers and percentages of Americans identifying of English ancestry from 1980-2010 based on the Census and American Community Survey:
1980 49,598,035 26.3%
1990 32,651,788 13.1%
2000 24,515,138 8.7%
2010 25,927,345 8.4%
I would expect some decline in the percentage, but the decline of 24 million in absolute numbers cannot be explained by demographic changes. Part of what’s happening is that most English ancestry is from colonial times and it’s not very salient. Many of these people end up identifying as of American ethnicity or with another ancestry where they have a more recent ancestor, even if it only makes up a small portion of their ancestry. This is an example of why I don’t think this information will really be useful. Another point- I don’t have a cite offhand, but I’ve read that Irish ancestry tends to get overstated.
The other thing I wanted to bring up is ethnic attrition among people of Hispanic ancestry. According to the Pew Hispanic Center, about 2% of the total U.S. population is of partial Hispanic, Latino, or Spanish ancestry but does not identify as Hispanic. Hispanics have a high intermarriage rate and, by the third generation, a solid majority of descendants of Hispanic immigrants have non-Hispanic ancestry as well. Only 35% of married third-generation Hispanics have a Hispanic spouse, compared to 63% of the second generation and 93% of Hispanic immigrants.
To tie this all together, let me use myself as an example. Three of my grandparents were born in the United States and nearly all of their ancestry goes back to colonial times. Based on genealogy research, as best I can tell, a solid majority (but not all) of that appears to be of English origin. My other grandparent is a Spanish-speaking immigrant from Central America. Like most Central Americans, that grandparent is of European and Native American ancestry.
In the 2010 census, I checked yes for Hispanic and indicated which country and then white for race. Confronted with the 2020 census, I would do the same and indicate English as origin underneath the race response.
A little bit of anecdata- In 2010, I was a census taker and I got a few interesting responses. About half of Hispanic respondents would try to give a Hispanic origin as a race. We were are instructed to repeat the instruction that Hispanic origins are not races. If they insisted after that, we were told to check “some other race” and write in their response. Some people just couldn’t get the distinction we were trying to make. One other response that comes to mind were the people who made me write in “Arab-American” even though they had a sheet of definitions that said that counted as white. i just did it and my understanding is that would be re-coded as white when they tabulated the data.