Answer
Demons are mentioned numerous times in the Bible. The Old Testament refers to them directly as “demons” (3 times), “evil spirits” (8 times), or sometimes in a more obscure sense such as “prince” (in Daniel 10). The New Testament mentions demons many more times, calling them either “demons” (daimónion) or “evil spirits” over 80 times. The origin of demons is not explicitly addressed in Scripture, but there are clues.
The etymology of the Hebrew and Greek words used to denote demons indicate that demons, in general, are powerful entities that transcend ordinary experience and the space/time physical nature of humanity; i.e., they are incorporeal beings.
Scripture suggests in Revelation 12:4, 7 that demons were originally created as angels and existed as part of God’s angelic army. However, when Satan rebelled against God, one third of the angelic host joined him in his revolt, which is why Scripture refers to them collectively as “Satan . . . and his angels” (Revelation 12:9). Most likely, these fallen angels who rebelled with Satan are the beings Scripture refers to as “demons.”
Again, the Bible does not specifically say where demons came from, so we cannot be dogmatic. What the Bible is clear about is the demons’ destination: “eternal fire” was prepared for them (Matthew 25:41), and they know of their coming fiery torment (Matthew 8:29).
