The Rev is basically a big symbol of all the nastiness that can come along with religion. He's heavy on the hellfire, easy on the forgiveness, and has pretty much everyone in town under his thumb. When people wriggle out of his grasp, like Bert does, their punishment is swift and severe. His harshness, however, loses him his daughter.
Besides Drummond and Bert, Hornbeck is The Primo Evolutionst in the town during the trial. A big-city journalist, he is a fast-talking joker who thinks that small-towners are there for his personal amusement. He's disappointed in Drummond at the end of the play for showing compassion for his opponent. As it turns out, this dude is just as intolerant as the townspeople.
Poor Mrs. Brady's function in the play is to follow her husband around, begging him not to eat too much and telling him that everyone loves him. Even when they are actually laughing at him.
Mrs. Brady calls her "Mother," and that's basically the role she plays for him. All this gal does is spoil and worry over her man. Not such a feminist character, in our opinions.
Meeker, the bailiff, is a sweet, easy-going guy; he doesn't come right out and say it, but he seems to be on Bert's side in the trial. The Judge is a weak representative of this hallowed profession, first heavily favoring Brady in the trial, and then caving in when the Mayor asks him to go easy on Bert in sentencing (to avoid a scandal).
Tom Davenport is the local district attorney, who is heavily overshadowed by Brady. Mostly, he just tries to keep up.
Melinda and Howard are two local young people whose role in the play is to show what the general public thinks of evolution. Howard accuses Melinda of being an ex-worm, and the granddaughter of an ape; she calls him a sinner.
These misconceptions of evolution are representative of what many people thought back in 1955… And some people still think today.
The townspeople seem to see the whole trial as a show. In fact, they basically settle right into their theatre seats and enjoy the spectacle. They are obedient followers of the Reverend, although some of them applaud Bert's speech, and seem to have some doubts about their beliefs by the end of the play.
Really, the townspeople seem to enjoy the chance for an Eskimo Pie and some diversion from their everyday lives. Watching these big city lawyers battle it out in their town courthouse provides them with that distraction.