http://www.herealittletherealittle.net/index.cfm?page_name=Demons

The article in the above site is more informative on demons and fallen angels than my previous response, explaining the difference between them.

 It appears that the case can be made from Scripture that the fallen angels were in existence before the demons, since the demons are the spirits of the dead Nephilim. The Nephilim were the giant offspring of the mating of the fallen angels, who were cast out of heaven with Lucifer, and the daughters of mankind.

The sequence appears to be: Lucifer -- Fallen angels -- Mankind -- Nephilim --  demons

If this understanding is not correct, please correct me, since I am not an expert.

Thanks.

Robert