One would argue that it is an ordinary town in that it has nothing that makes it especially unique among other small, rural American farm towns. It has a main street, small shops, a post office, and is not too far from a train station. It is surrounded by farms and populated mostly by the people who run those farms, simply country folks. The town is religious and family-centered, as were most small towns in the midwest of the time.
What makes it different is a bit more difficult to answer given I am unsure what we are comparing it to. Other small towns? Big cities? It is fairly similar to other small towns, and for obvious reasons it is very different than big cities. The one distinguishing difference for Holcomb is that after the murders it becomes known for this crime. Just as we have seen in so many towns and cities that are associated with a high profile crime (Columbine, Colorado and Waco, Texas come to mind), the area becomes forever linked to the crime - making it tragically different than other similar towns and cities.