Most of the figures are taken from the CIA Factbook or PEW Research Center Surveys.
According to the CIA Factbook and the Pew Research Center, the five countries with the largest number of Catholics are, in decreasing order of Catholic population, Brazil, Mexico, the Philippines, the United States, and Italy.
The country where the membership of the church is the largest percentage of the population is Vatican City at 100%, followed by East Timor at 97%.
According to the Census of the 2019 Annuario Pontificio (Pontifical Yearbook), the number of Catholics in the world was about 1.313 billion at the end of 2017. The research initiative Catholics & Cultures compiles data on Catholic demographics, including from the Annuario Pontificio, by country.
Conflicting numbers can be found in 2013 research conducted by the Brazilian polling institute Datafolha. This report states that the percentage of the population in Brazil of Catholic religion, over the age of 16 years, is just 57%, in contrast to the 64.63% published by CIA and to the 68.6% of Pew Research Center. Also, the 2010 Mexican Census showed this percentage to be 83.9% – against a 91.89% number in the CIA World Factbook.