I don't know how I missed this message in October. I am related to most of the Humphreys' of Llanddwywe uwch y graig (The family mentioned by Peterej above include my great grandfather and great great grandparents) So I would be interested in any connection between your family and mine.
There is a John S (possibly D) Humphreys in the 1920 USA Census living at Salem Ward 6, Marion, Oregon His age is smudged, it is either 48, 45 or 43 (so estimated birth year: abt 1872 or 1875 or 1877). John was born in Pennsylvania; both his parents are from Wales
In the same household is Lula W, John's wife age 37 from Oregon
and 3 children, Sophia E aged 5, Jesse H aged 3 years 10 months and Norman P who is 2 years and an indecipherable number of months.
If John was born in the 1870's in Pennsylvania, he should be on the 1880 USA Census. The only one who seems to fit the bill is John H. Humphreys
Aged 9 (abt 1871) in Philadelphia, Pennsylvania the son of Roland (aged 43) and Harriett (aged 40) Humphreys. John also has a 5-year-old brother Frederick.
Harriett's unmarried sister Elizabeth Howes is also living with the family, so we can assume that Howes was Harriett's maiden name. Harriett's parents were both born in England
The 1900 Census says that Roland and Harriett emigrated in 1869 and had been married for 30 years, so they either married just before or just after emigrating and will not be found on a Welsh Census as a married couple.
If Roland and Harriett are the parents of your John, it doesn't look like the family hailed from Llanddwywe uwch y graig. The only Rowland Humphreys on the 1851 Wales Census born about 1837 is Roland the son of Edward & Margaret Humphreys aged 17 (or 19) in Trederwen Montgomeryshire.