Objection 1. It would seem that the angels will be judged at the coming judgment. For it is written (1 Corinthians 6:3): "Know you not that we shall judge angels?" But this cannot refer to the state of the present time. Therefore it should refer to the judgment to come.
Objection 2. Further, it is written concerning Behemoth or Leviathan, whereby the devil is signified (Job 40:28): "In the sight of all he shall be cast down"; and (Mark 1:24)* the demon cried out to Christ: "Why art Thou come to destroy us before the time?" for, according to a gloss, "the demons seeing our Lord on earth thought they were to be judged forthwith." [The reference should be Matthew 8:29: 'Art Thou come hither to torment us before the time?' The text of Mark reads: 'Art Thou come to destroy us?'] Therefore it would seem that a final judgment is in store for them.
Objection 3. Further, it is written (2 Peter 2:4): "God spared not the angels that sinned, but delivered them drawn down by infernal ropes to the lower hell, unto torments, to be reserved unto judgment." Therefore it seems that the angels will be judged.
On the contrary, It is written (Nahum 1:9) according to the Septuagint version: "God will not judge the same thing a second time." But the wicked angels are already judged, wherefore it is written (John 16:11): "The prince of this world is already judged." Therefore the angels will not be judged in the time to come.
Further, goodness and wickedness are more perfect in the angels than in men who are wayfarers. Now some men, good and wicked, will not be judged as stated in the text of Sentent. iv, D, 47. Therefore neither will good or wicked angels be judged.
I answer that, The judgment of discussion nowise concerns either the good or the wicked angels, since neither is any evil to be found in the good angels, nor is any good liable to judgment to be found in the wicked angels. But if we speak of the judgment of retribution, we must distinguish a twofold retribution. One corresponds to the angels' personal merits and was made to both from the beginning when some were raised to bliss, and others plunged into the depths of woe. The other corresponds to the merits, good or evil, procured through the angels, and this retribution will be made in the judgment to come, because the good angels will have an increased joy in the salvation of those whom they have prompted to deeds of merit, while the wicked will have an increase of torment through the manifold downfall of those whom they have incited to evil deeds. Consequently the judgment will not regard the angels directly, neither as judging nor as judged, but only men; but it will regard the angels indirectly somewhat, in so far as they were concerned in men's deeds.
Reply to Objection 1. This saying of the Apostle refers to the judgment of comparison, because certain men will be found to be placed higher than the angels.
Reply to Objection 2. The demons will then be cast down in the sight of all because they will be imprisoned for ever in the dungeon of hell, so that they will no more be free to go out, since this was permitted to them only in so far as they were directed by Divine providence to try the life of man. The same answer applies to the Third Objection.
Source: Summa Theologica (New Advent)