Onderdonks and Blauvelts and Tourneurs! Oh my!

Frozen River at Sunset

Rockland County is a wedge of farmland and forest only a few miles north of New York City. It's situated directly across the Hudson River from the legendary Tarrytown in Sleepy Hollow, the home of the Ichabod Crane and Headless Horseman. As with Sleepy Hollow, the Dutch first settled the Rockland County region, founding its many small farms and villages.

Although the Dutch surrendered to the English in 1664, for most of its history the area was dominated by families of Dutch and French Huguenot ancestry. Some of the families that moved into the vicinity in the late 1600s were named Tourneur, Oblenis, Low, Vleckerands, Hennion, van Vorst, Blauvelt, van Schyven, Baldwin, Onderdonk, Griswold, van Houten, and Lighthizer. Most of these families could easily be traced to the earliest days of the New Amsterdam settlement in the 1500s.

According to some 19th century genealogies, my wife, through her mother's mother's father, Russell Tenure (1892-1954), was descended from these old Rockland County families. However, using actual government and parish records, I could only really confirm the family tree back to wife's 4th great grandfather, Michael Tenure (1797-1863). While these old 19th century genealogies were written with great authority, they offered little corroborating evidence.

I was hoping DNA could provide us with that evidence when I first tested my mother-in-law's DNA on 23andme. Unfortunately, it proved very difficult to identify common ancestors with any of her genetic cousins, in Rockland County or elsewhere. There were a couple reasons for that problem:

1. The last few generations of her family were comparatively small. My father has hundreds of 3rd, 4th, and 5th cousins. My mother-in-law has a few dozen. Fewer cousins mean fewer close genetic matches, leaving only more distant relatives. It's much more difficult to find a 5th great grandparent than a 3rd great grandparent, especially when few people have complete family trees, including me.
2. My mother-in-law is 1/4 Jewish from her maternal grandmother's side. Some populations, such as Jewish people, have suffered through multiple "bottlenecks", where their population fell to a small number of individuals, which then intermarried. If your parents are 3rd cousins then your 4th great-grandparent is really your double 4th great grandparent, meaning that you share more genetic material with any of their decedents. This means that people of Jewish ancestry often dominate any list of genetic matches. Unfortunately, I am unable to trace that family branch back further than the mid 1800s, likely because of name changes.

Even though there were good reasons for not finding the common ancestors of genetic matches, I was beginning to worry that there was a mistake in the family tree or even that there was a non-paternity event. However, this latest Ancestry.com test has put my worries to rest, Ancestry.com is more focused on geneaolgoy and most matches have passable to excellent family trees. So, finally, I have matched some of her genetic cousins.

My wife has several genetic cousins that share Onderdonk, Blauvelt, and Tourneur ancestry in Rockland County and several other Dutch surname matches around New York. I've managed to find common ancestors for each of these Rockland families, although it is still difficult to claim any specific ancestor is confirmed by DNA. 

These families, along with several other old families in the region, often intermarried so it's sometimes difficult to define the precise source of the shared DNA. In one instance, I found a distant Blauvelt cousin who also shares Onderdonk ancestry, making it difficult to determine which of their common ancestors passed down the DNA. 

Still, I've confirmed that my mother-in-law is the quintessential New Yorker, whose maternal grandfather's family history reaches back all the way to the beginning of the New Amsterdam. That was certainly nice to put to rest. For once, those old 19th century genealogies were right.

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