This might seem a silly question but...

[jimrtex]

How I can get a horizontal table with total population and Welsh ancestry for every U.S. county at once is beyond my capabilities on the Census web site, unfortunately.  I've so far been unable to find a site that does this.  If I do find one, I'll let you know.

With American Fact Finder, when you get to Geography, select Geo within Geo.  You can then choose all Counties in US.  Ancestry is in the SF 3 data set.

[jimrtex]

English is very much an Indo-European language.

Btw, English is the first language of the overwhelming majority of people in Wales. Has been since the 19th century.

I'm very much aware of both of those, and should have said "non-English."  But in an area like Oneida County, people are not going to identify as culturally Welsh; they identify as culturally Mormon.  And even if some did, 20.8% is not enough to have the described effect on local politics.

Malad Valley Welsh Festival

Founders of the town of Samaria included James Thomas, Thomas Roberts, David Davis, and Taliesen Hughes.   An annual eisteddfod was held until WWI, alternating between the two towns of Samaria and Malad.  The Welsh Festival was began in 2004 as a revival of that earlier event.

Tiny US town's big Welsh heritage