It was during the year of the conquest of England  that a fellow named Roger de Montgomgery was created Earl of Shrewsbury and Arundel. It was in the French, English, and Latin languages that this area became know by his name, Montgomery. It was of course still part of the ancient Welsh Powys, but you know, to the victors go the history books.
The first JONES I could find was Lewis Jones.
The English legal records list a "Richard Joones" [1547-1551] dealing with land in Llanfechan at the bequest of Griffith Jones. [Bundle 1238/ no. 56-60 ]. During this transition period the Norman spelling "Jevan"
is frequently used as in "Edward ap Jevan" and "David ap Jevan". It would seem that the spelling "Jones" was established consistently by 1558.