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.
The bruises and cuts on Reese Witherspoon are real, since the actress had an accident shortly before shooting began. Instead of covering them with make-up or wait until she healed more, Jeff Nichols decided to film her like that because it suited the character.
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.