The percentage of Americans with no religious affiliation at all (the "nones") has been growing with each new generation. That is just an undeniable fact. The current percentage of these "nones" in the United States as a whole is 22%, but it much higher among young Americans.
The chart above, from the Public Religion Research Institute, shows the percentage in the largest cities in each area of the country. Note that the cities with the least number of self-declared "nones" are in the South. I'm not at all sure that area has less "nones" than other parts of the country -- just that it is harder to be an open "none" in the South, because those people must pay a higher social cost than in other areas.
At any rate, the number of non-religious people has been growing for decades now -- and there is no reason to believe that won't continue in the future.
