The movie is based on actual events, as explained in the 2008 book "The Wettest County in the World" by Matt Bondurant, grandson of Jack Bondurant.
Tom Hardy's character was originally supposed to be slimmer but Hardy had to bulk up for The Dark Knight Rises (2012).
Shia LaBeouf drank moonshine in order to gain as authentic an appearance as possible. By his own admission, his drinking and over-aggressive attitude caused co-star Mia Wasikowska to try and leave the film. He also stated that Tom Hardy maintained his sobriety throughout the shoot, and gave a better performance.
According to director John Hillcoat, Tom Hardy actually saw his character as a maternal figure and many of the characters manners were modeled on Granny, from Friz Freleng's Loony Tunes series.