Henry Harpending confirms:
When responding to the Census, more than five million Americans claim to be of Dutch descent. And they mostly are, at least a little. Now you might wonder how they compare with the Dutch back in the Netherlands: you might wonder about the relative academic or economic success of these two groups, which presumably have a common ancestry. But you would be wrong to do so. You would be comparing apples and House of Orangemen.
There were four or five different Dutch waves of settlement in this country. The first is pretty well-known, the Dutch colony in New York. Of course, it was only about half Dutch in origin: the rest were Walloons and French Huguenots. Lots of people have some ancestry from that group, including people I know. Why, if there was any justice, Henry Harpending would own a fine farm on Manhattan Island right now.
Of course, Henry isn’t all that Dutch. His surname is. He comes from an area of New York State that really did have some Dutch settlement. The thing is, white Protestants in this country have been intermarrying rather freely for several hundred years: it is rare to find someone in that category whose ancestors all come from one ethnicity. I would be surprised if Henry is 1/8th Dutch. In much the same way, my patrilineal lineage is Ulster Scot (who fears mention the battle of the Boyne!?) but the rest includes English, Welsh, Scottish, Green Irish, and a component that, I suspect, only became Dutch in 1918, and was Bavarian before that. We’re talking about ye olde Americans, not Ellis Island types. Not that they haven’t mixed as well, but less so… [. . .]
Most of the people who self-identify as Dutch-Americans are mostly something else. Why? Sometimes a family tradition, or a surname, but more than anything else, fashion.
Fashions change. For example, the fraction of Americans who report English ancestry has dropped drastically since 1980 – so much that so that you would have to wonder about secret death camps if you took it seriously. But it’s fashion. I looked at the census numbers for my home county, and then looked at the phone book: Census result was 20% English ancestry, real number was more like 80%. Of course this means that people in the US claiming a particular ethnicity can not only have limited ancestry from that group, but be oddly unrepresentative as well.
I would probably put “Dutch” on a census form if an answer were required. I am either 1/32 or 1/64 Dutch, and worse the supposed Dutch ancestor was a Huguenot or something like that, so I am likely really 0% Dutch. No matter…….I've commented on this phenomenon before (e.g.), but a periodic reminder is useful. I don't see a problem with someone identifying with his patrilineal national origin for census purposes while remaining aware of his overall ancestry. What I find irritating is the eagerness of some with American ancestry to identify as "Scotch-Irish" after reading a review of Albion's Seed, or "Celtic" in the name of Celtic Southronism, or "German" because they had a German great-grandfather, and then declare themselves at war with or at least safely distinct from evil/culpable "WASPs" / "Anglo-Saxons" (which appellations in reality describe the core of the breeding population from which the newly self-identified Borderer/Celt/German sprung).