Demons will be judged one day for their rebellion against God and the evil they have committed against mankind. The Bible says that Christians will judge demons on that day.
3 Do you not know that we shall judge angels? (1 Cor. 6:3)
6 And the angels who did not keep their proper domain, but left their own abode, He has reserved in everlasting chains under darkness for the judgment of the great day; (Jude 1:6)
Some demons are in chains in hell at this very moment. Some, like Satan, have been allowed to roam the earth and possess people as previously mentioned.
What a great honor it will be for Christians to judge these terrible creatures who sought to overthrow God and inflict much harm on mankind.
The Eternal Destiny of Demons
Demons know what their final end will be.
28 When He had come to the other side, to the country of the Gergesenes, there met Him two demon-possessed men, coming out of the tombs, exceedingly fierce, so that no one could pass that way. 29 And suddenly they cried out, saying, “What have we to do with You, Jesus, You Son of God? Have You come here to torment us before the time?” (Matt. 8:28-29)
After their judgment, these demons, as already noted, will be cast into the lake of fire which was prepared by God for them to receive eternal torment. Although they are spirits, their substance is such that they can feel great pain and torment.
41 “Then He will also say to those on the left hand, ‘Depart from Me, you cursed, into the everlasting fire prepared for the devil and his angels: (Matt. 25:41)
10 The devil, who deceived them, was cast into the lake of fire and brimstone where the beast and the false prophet are. And they will be tormented day and night forever and ever. (Rev. 20:10)
The lake of fire will not only be where demons will endure eternal torment and suffering, it will also be where every person who did not believe in Jesus Christ will suffer this torment too. Only the saved, Christians, believers in Jesus Christ, those who are found in the Book of Life will escape the wrath of God.
14 Then Death and Hades were cast into the lake of fire. This is the second death. 15 And anyone not found written in the Book of Life was cast into the lake of fire. (Rev. 20:14-15)
36 He who believes in the Son has everlasting life; and he who does not believe the Son shall not see life, but the wrath of God abides on him.” (John 3:36)