Here's the ancestry profile for Rockland County, NY (31.4% Jewish):
https://statisticalatlas.com/county/...ounty/Ancestry
How do you get 31.4%?
Polish -- 4.7%
European -- 4.3%
Hungarian -- 3.6%
Russian -- 3.6%
Eastern European -- 1%
Austrian -- 0.8%
Israeli -- 0.7%
Ukrainian -- 0.7%
Total ancestry: 19.4%
And that's counting some heads more than once AND assuming that there aren't any Catholics among those Poles, Hungarians, etc.