''Taking a half-full approach, you could rephrase that to say that of the three commonest white ancestry groups in the U.S.A., two are from the British Isles and the third is from the nation of which Anglia and Saxony are both regions. That's a total 34.7 percent on the 2000 Census figures (page 3 here).
Why stop there? You can add in the 7.2 percent of census respondents who gave their ancestry as "American," since doing so is a trait restricted almost entirely to the Scotch-Irish. Add in those who actually did respond with "Scotch-Irish" (1.5 percent) or "Scottish" (1.7 percent), and we're up to 45.1 percent.''
Read the whole thing at the link.
And incidentally, I found the maps below which indicate ancestry and ethnic group. Some are rather dated, such as the first one, based on 1990 Census figures. (Click to make maps bigger).
Then there is this one:
English ancestry looks to be surrounded by every other ethnic group, but as Derbyshire says in the article, many of those (as in the 'red' states shown above) claim ''American'' as their ethnic identity, which is often a sign of colonial-era British/ Anglo-Saxon ancestry.
The frequent claim by people of German descent that their group is the most numerous is easily challenged. Just as many people say of English-descended Americans, few are of 'pure' German origin, most families having various European ethnicities in their family tree, especially in the Northern tier states which are so solidly blue above. And again, many people selectively identify with a small portion of their overall ancestry. Just now, nobody wants to be English or Anglo-Saxon.