I would say that the trial being set in Hillsboro is extremely important. Its rural and traditional setting becomes the perfect backdrop to fully grasp the fundamental conflict at the time between scientific explanations and religious interpretation. The time period being a moment where scientific explanations were supplanting the accepted traditionalist approaches helps to heighten the tension that is felt between Bert Cates and the rest of the town, especially Reverend Brown. I think that the escalation of tension in the courtroom throughout the proceedings helps to bring the drama between this collision between both of these polarities. The historical element present might not be well suited to be treated as pure historic fact, as much as exploration of the tension between both philosophical premises in a moment in American History, which certainly has had and does have some challenges at moments with the reconciliation between science and religion.
The setting in many ways is vital to the story as it was chosen by the real town that they would be the place to have this debate take place in the form of a trial. It provides a great deal of drama for the movie as well given that it takes place in the South, always seen as a hotbed for revivalist and evangelical religious feeling, some of the main opposing forces to the idea of teaching evolution in schools at the time.
The setting also provides another element of conflict as it pits the Northern lawyer against the southern one, and two mindsets of the two different regions against each other as well.