- Patrick Stump (lead vocals, rhythm guitar)
- Pete Wentz (bass guitar, lyricist)
- Joe Trohman (lead guitar)
- Andy Hurley (drums)
Patrick Stump and Pete Wentz were raised Catholic and attended parochial school. Joe Trohman and Andy Hurley were not raised in any religious tradition.
Wentz has written about his Catholic upbringing and how it has influenced his music, including the song "The Mighty Fall" from Fall Out Boy's 2005 album From Under the Cork Tree. In the song, Wentz sings about how he lost his faith in God and the Catholic Church.
Stump has also written about his Catholic upbringing and how it has influenced his music, but not as explicitly as Wentz. In the song "Save Rock and Roll" from Fall Out Boy's 2013 album of the same name, Stump sings about how the Catholic Church has lost its way and is no longer a force for good in the world.
Trohman and Hurley have not written about their religious or non-religious upbringing.
In conclusion, the members of Fall Out Boy have various religious backgrounds and beliefs. Patrick Stump and Pete Wentz were raised Catholic, and their upbringing has influenced their music. Joe Trohman and Andy Hurley were not raised in any religious tradition.