An excellent report from the 1964 Blog.
Pope Francis is making a Lenten season trip to Mexico this week (Feb. 12-18). Since 2010, approximately 82% of adult residents in Mexico have self-identified their religious affiliation as Catholic in national surveys, on average. This is equivalent to a population of about 97 million self-identified Catholics of all ages as of 2013, the most recent year for which Vatican statistics about parishes, priests, and sacraments are available (the self-identified Catholic population is estimated to have been 99.8 million at mid-year 2015). The Catholic affiliation percentage has fallen from where it was in the 1980s. In that decade, approximately 88% of adults self-identified as such. However, Mexico’s total population has grown and even with this lower affiliation percentage there were 42 million more Catholics in Mexico in 2013 than in 1980 (63% growth).
The percentage of Mexican Catholics saying that they attend Mass every week has declined in surveys from an average of 58% in the 1980s to 44% in the 2010s. However, once again, a declining percentage does not mean that there are fewer weekly attenders in the pews. With population growth the number of weekly Mass attenders has grown from 36.7 million in 1980 to 42.7 million in 2013 (16% growth). Given the number of parishes in Mexico in 2013 and the self-reported Mass attendance of survey respondents, we would estimate that there are 6,064 weekly attenders per parish.
Since 1980, Vatican statistics indicate that Mexican dioceses have added a net total of 3,072 parishes (77% growth). This additional infrastructure has made it possible to decrease the number of Catholics per parish slightly, even with population growth, from 15,932 in 1980 to 13,782 in 2013. These numbers are based on the size of the Catholic population as we see in national surveys rather than the Church’s own population estimates, which have been somewhat unreliable in Mexico.