Association of Religion Data Archives (ARDA)
http://www.thearda.com/
The ARDA contains many datasets pertaining to religion, such as surveys on topics such as the public's religious attitudes and practices, surveys of church leaders, and studies on the provision of social services by individual congregations. ARDA also provides geographic profiles of congregations and demographic profiles of denominations. While its primary focus is on the United States, ARDA also has much comparative/international data on religion, including single-nation studies on topics such as spirituality and health, cross-national surveys on topics such as the role of religion in political life, and cross-national data on matters such as religious populations and measures of religious freedom. Researchers should go to the Data Archive for a directory of the different studies available.
International Data Base
https://www.census.gov/programs-surveys/international-programs/about/idb.html
As part of the Census Bureau's International Programs, the International Data Base (IDB) contains statistical tables of annual demographic data for 227 countries and areas of the world, covering topics such as population distributes by age an sex, components of population growth, morality, and life expectancy.
World Population Prospects
https://esa.un.org/unpd/wpp/
This database is produced by the United Nations' Population Division and contains cross-national data on basic population demographics and vital statistics (e.g. birth and death rates, maternal mortality, population by age and gender and urban/rural areas, median age of population). See http://www.un.org/en/development/desa/population/publications/dataset/index.shtml for other data from the Population Division, cover topics such as migration, fertility, marital status, and population policies.