Reese Witherspoon had an accident shortly before filming started; her bruises and cuts are real. Instead of covering them with make-up or waiting until she healed more, Jeff Nichols decided to film her like that because it suited the character.
Tom Blankenship's name came from a real person that Mark Twain based his character, Huckleberry Finn, on. Blankenship, in real life, is rumored to later became a judge, but no one knows for sure his fate.
Galen, played by Michael Shannon, points out a working ceiling fan he found in the river. In Jeff Nichols previous film Shotgun Stories, Son Hayes, also played by Michael Shannon, is sitting on a dock in front of a ceiling fan presumably found in the river.
At the start of the film where the two boys meet Mud, Neckbone is wearing a shirt with the word 'fugazi' on it. In the Wolf of Wall Street, another film starring Matthew McConaughey, there is a scene where his character tries to explain what a Fugazi is to Leonardo DiCaprio. Quote: Fugayzi, Fugahzi, it's a wahzi, it's a woozie, it's a (whistles) fairy dust. The shirt is actually a band tshirt. Fu-gah-zee is Italian for fake.