In graduate school papers, it's not sufficient to make vague generalizations about demographics. You can't just write "there are a lot of X religious group in area Y." Instead, identify the specific region (city, county, state, country) and then check these databases or an atlas to discover the real or estimated percentages that you can include in your paper.
CAREFUL: Make sure to footnote those statements, and cite the database where you found the statistical data!
The World Religion Database contains detailed statistics on religious affiliation for every country of the world. It provides source material, including censuses and surveys, as well as best estimates for every religion for the period 1900 to 2050.