Looks like twenty people wrote the script and gave up at the end.

Rating: 1/10 (30 July 2018)

Divorced woman (Frances McD) whose daughter was raped and set on fire hires three billboards (conveniently in her road) to goad the police chief (Woody H) into action after several months of nothing.
Sadly, the police chief is dying of pancreatic cancer, and his deputy (Sam R), who is a racist sociopath with a heart of gold, decides to set the billboards on fire, throw the billboard agent out of his window, and arrest Frances McD's boss on marijuana possession.
Meanwhile Frances McD has assaulted the dentist with his own drill, Woody H has shot himself, and a random stranger threatens Frances McD in her gift shop, just before Woody H's wife turns up with his last letter to her.
Wow! A lot of story there, hey? Makes you think that you're in for a fantastic ending, don't it? What actually happened is that the fifty or so people writing this all got tired of thinking up more and more destructive turns and sick characters á la Coen brothers (which this isn't a patch on), and realised they had to conclude it. Unfortunately they didn't manage to.
Now if it had turned out (as was probably in the ninety-fifth draft) that Woody Harrelson had been the rapist in the first place (believable, seeing as all the other cops are suffering with major anti-social personality disorder), some sort of resolution might have been achieved. As it is, we share Frances McD's complete lack of closure. Was that the point? Highly overrated film, give it a miss.
Seen Olive Kitteridge? Frances McD reprises Olive, except here she acts out - firebombing the police department, among other stuff.