Americans used to farm a rich variety of crops. Some were very labour intensive, requiring neighbourly cooperation. In these counties, parents were more likely to give their children names that were common. This may indicate a desire for conformity. By contrast, in areas where farmers could be more self-sufficient, they chose names that were more individualistic. And when exogenous shifts propelled farmers into economic autonomy, they became even more self-expressive.
Agricultural intensity negatively correlated with individuality, you mean.