In the 21st century, the demographic trends in the United States have started to change. There's numerous reasons for the changes, with some being the migration, birth rates, medical advancements.
The population of the United States is slowly aging. Despite the migration constantly increasing the population, the people are still becoming older and older on average. The reason for this is the low birth rates, as well as the migration of mostly people that are between the ages 20 and 35.
Also, there's changes in the ethnic and racial distribution of the population, as the white population is slowly becoming less and less in total percentage, while the Latino population being a very fast growing one. The Latino population has bigger birth rates than the other groups. Also, most of the migrant are from countries of Latin America. And the constant rise of their number also results in the constant rise in the number of Catholics in the United States.