I researched variations of Manley, Manly, Munnelly and Monnelly in the 1856 - 1857 Griffiths. With a few exceptions only one form of the name was recorded in each parish. The name is concentrated in a 7 by 7 by 5 mile triangle bound by Ballina, Crossmolina and North. It is confined West of the Moy River. I concluded the name originated in the area.
Only a handful of people used Manley or Manly in that area that time. I can only find one person who I think was an 'English Manley'. If you Google Munnelly and Mayo you find real people living there today using the original name. If you Google Manley Mayo you find people like us whose relatives emmigrated long ago and changed their name. As a result it may appear that the name Manley is dying out. It may be that Manley has never been widely used in the area.
There were two men named John Manley or Manly in 1856, A man I call "John the Farmer" and another "John in the Alley" Others were named John Munnelly or Monnelly. I know now for certain that my John left at lease five years earlier. There was a third John Manley, "John the Voter" who owned a small amount of land which allowed him to vote. He was on the voter roles in 1850. He was gone by 1856 or lost property. It is possible this man left the country and is someone's ancestor.
I do know that my John, let's call him "Paul's John", had a father named Patrick who was a farmer. He moved to Stamford, England and appears to have sold clothing in the market there.