Mildred Hayes
Mildred is the protagonist of the movie. She is both victim and aggressor, depending on whose eyes she is seen through Still in the early stages of grief after the brutal rape and murder of her daughter Angela. At first, Mildred believes that her daughter's killer will be caught but now she is frustrated by the lack of movement on the case. She fears that Angela has been forgotten and that what was done to her should be far more important to the citizens of Ebbing than it actually is. She also feels that the police have been sitting on their hands and waiting for the case to solve itself.
Mildred is judged very harshly by her fellow Ebbing residents. They don't seem to see the depths of her anguish and instead react very badly to the billboards that she puts up. It is as though they want to be allowed to forget Angela and Mildred's actions are forcing them to confront a horror they would rather move on from. Mildred is a fierce defender of her daughter and wants justice. She refuses to be silenced despite the increasingly threatening behavior of those around her. She stands her ground.
Mildred is about to cross the line between determined and dogged quest for the truth and a thirst for vigilante justice. She has begun to position herself as an avenger of all raped and murdered young women by the end of the movie and is fighting with herself as to whether or not she will go through with the plan that she and Dixon have made to drive to Idaho and kill a man they know to have raped and murdered another young woman.
Chief Willoughby
Willoughby is a good man. While he is rather irritated by the billboard that is a slight on his character, he is extremely sympathetic towards Mildred and leaves her a letter explaining that he tried to find out who killed Angela, and that he wishes he could have brought her justice. Willoughby has terminal pancreatic cancer and kills himself rather than put his family through the agony of watching him die from the disease. He makes it known in letters to various people that the billboards had nothing to do with his decision to commit suicide.
Officer Jason Dixon
Racist, bigoted, and an alcoholic with a mean streak and a bad temper, Dixon is difficult to warm to. He wants to be a detective but his behavior and his hatred for all in general is preventing him from achieving this goal. After the Chief dies, he reads the letter that was left for him and learns that he needs to come from a place of love in order to succeed. He teams up with Mildred in an unlikely alliance fueled by a determination to catch both Angela's killer and the man whom Dixon overheard bragging about raping and murdering a girl in Idaho.
Red Welby
The owner of the billboards, Welby feels sorry for Mildred and rents her the unused billboards at a discounted rate. He then bears the wrath of the community for it, and gets assaulted by a drunk and angry Officer Dixon.
