Christianization of Poland
Wikipedia
https://en.wikipedia.org/wiki/Christianization_of_Poland
Evangelical Poland
Poland
Joshua Project
https://joshuaproject.net/countries/pl
Poland: Religion Demographics, Data Of A Very Catholic Country
Expats Poland
https://www.expatspoland.com/poland-religion/
Protestantism in Poland
Wikipedia
https://en.wikipedia.org/wiki/Protestantism_in_Poland
Religious practice declines significantly in Poland, especially among young, finds study
Notes from Poland
Major Religions In Poland
World Atlas
https://www.worldatlas.com/articles/predominant-religious-beliefs-in-poland.html
Religious affiliation in Poland between 2015 and 2018
Statista
https://www.statista.com/statistics/1139984/poland-religious-affiliation/
Religion in Poland
Wikipedia