Three very good sources of reference are the book "A Land Unknown: Hell's Dominion" by B.W. Melvin and the websites Bibleprobe.org and testimoniesofheavenandhell.com. You should take the time and read that book and visit the websites, if you are interested in those kinds of accounts.
In his book, Bryan Melvin states that he saw beings chained up in a cavelike structure as well as demonic creatures going up and down between the earth and hell. Who are those creatures that are chained up? Are they demons? Why are they chained? Is it maybe because they are the worst of the worst? I believe those that are chained are the fallen angels who have sinned- the ones who, when cast out of heaven, had sexual relations with women and as a result, giants were born. In 2 Peter Chapter 2 Verse 4 it says: "For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment." About the sinning of the fallen angels, in Genesis 6:2 it says: "That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose." The sons of God are believed to be the fallen angels. Now, in Genesis 6:4 it says: "There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown." The giants, or Nephilim, are believed to be the offspring of the fallen angels and human women.
Now speaking of the Nephilim, there are theories that they are the ones who are the demons. It is believed by most who embrace this theory that after the flood, God allowed the Nephilim's spirits to remain on this earth. It is a good theory, but myself, I am not sure if I believe it. Human beings will never become demons, and since the Nephilim were part human, I don't really believe that they became demons either. Again, it's a good theory, but not one that I subscribe to.
In short, I believe along with most believers (smile) that demons are the result of fallen angels. There are some who roam the earth, and some that are confined to hell. The ones confined to hell are the ones who had sinned, or defiled themselves with human women.
To know 100% without a doubt though, well, I'll just have to ask Jesus when I meet Him face to face. Then again, I won't have to ask. He'll already know that this is something I am wondering about.
What is your theory about where demons come from? Let us know!
WEEK OF JULY 23: The conclusion of the series (for now)-Demonic Attacks.