World religion database: international religious demographic statistics and sources
"The World Religion Database (WRD) 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 to offer a definitive picture of international religious demography. It offers best estimates at multiple dates for each of the world's religions for the period 1900 to 2050. The WRD also contains a feedback mechanism so that users can leave comments on sources or methodology related to any figure reported in the WRD. In addition, the WRD will be constantly updated with new sources of data as they become available, such as estimates of religious affiliation at the province level within countries and religious freedom information for all countries. "