Charles Finney perhaps? Thats an interesting question though. If most of the Appalachian people in the South from (Scots, Irish, Welsh & English linage) were originally all Calvinists, how did this transformation to Free Will take place?
Backwoodsy tent revivals which were heavy on emotionalism and light on theological depth contributed.
This spun off from Finney's revival.
I do not think it is a coincidence that Pentecostalism rose in this culture just as Calvinism went on the decline in SBC life.
There was a near full scale abandonment of thoughtful and scholastic conservative theology in this culture during this time.
It was also about this time that teetotalism grew to prominence- which is another evidence, imo, of the lack of scholarship among Christians in our country. The church had NEVER on a broad scale condemned the moderate consumption of alcohol before. This came with the rise of ignorance, imo.
KJV onlyism was not far behind.
Also about this time or a little thereafter Gospel music rose to prominence and replaced the dominance of the great, deep theological and rich hymns that we tended to use in worship.
Southern Gospel spawned from that and MOST of it, imo, is so shallow it is hardly worth nodding at, much less singing in worship services. NOT ALL OF IT MIND YOU!!! But let's face it- Gaither music cannot hold a candle to Isaac Watts and Charles Wesley. NOT THAT ALL GAITHER MUSIC IS SHALLOW!!!
We seemed to embrace ignorance and hold in disdain scholarship about the turn of the 20th century. Calvinism and scholarship tend to rise and fall together.