Your post peaked my curiosity about John Welsh. Palmerston is a town that is on the border of Perth County and Wellington County. In the 1871 census there are a few Welsh families living in the township of Maryborough, Wellington County. They are Irish. I could not figure out if your Welsh was Irish or Scottish from looking at census for South Dakota. John is a common name. Was he married to Myrtle?
Here is a link to a map of Wellington and you can see that Palmerston borders Maryborough and Minto Twps.
http://www.wcm.on.ca/archives_21.php