I think most recognize some of the inherent stresses of urban life, especially if you add poverty and racial discrimination to the mix. Of course, there are stresses that exist in rural and suburban settings, but some parts of urban life can be quite hard. Being anonymous in a crowd, the amount of violence, the pace of life, higher cost of living are just a few of these stressors.
So, are those who live in urban settings more prone to mental illness? Some doctoral student in Sweden looked at the association of Schizophrenia, population density, and neighborhood deprivation. What did he find?
Our results therefore suggest that it is not the adverse neighborhood conditions that cause the morbidity. Instead, it seems as if there are familial selection effects that draw high-risk individuals into densely populated/socioeconomically deprived neighborhoods. In other words, the same factors that explain residence in such neighborhoods also explain the increased risks for psychiatric morbidity. link to article here.
Does this make sense to you? Certain factors draw (or keep?) some families in deprived settings and those same factors explain increase mental illness risk? What would these factors be?
Musings on Faith and Psychology 
I think when you have the cycle of mental illness or trauma or abuse it makes the chances of the number being higher greater. Not to mention that many people never break free from their family and what damage it has caused. Which also perpetuates the cycle. For instance, an example, a mother is diagnosed as bipolar. Whether she is for sure or not is up for debate. But that mother spends her life hurting and harming her children through her illness. Those children grow up and while they may never have an actual mental illness they often believe they do or are told by family they do because they were never taught healthy ways of interacting with other people within a family. When your mother sleeps with your prom date, mental illness or not, that’s a serious boundary to cross. And when situations like that are “normal” to you as a child it’s hard to break those cycles as an adult. And often even if the children DO better than what they had they often over compensate the other direction which also leads their children to have issues as adults.
I have no idea if what I said even makes any sense. But when people are labeled in large groups with no other knowledge of something different. They are most likely going to follow the same pattern, mental illness or just bad behavior.