If I could poke my head into hell, would anyone be there?
Satan and the fallen angels would certainly be there:
Scripture speaks of a sin of these angels. This “fall” consists in the free choice of these created spirits, who radically and irrevocably rejected God and his reign. We find a reflection of that rebellion in the tempter’s words to our first parents: “You will be like God.” The devil “has sinned from the beginning”; he is “a liar and the father of lies” (CCC 392).
It is the irrevocable character of their choice, and not a defect in the infinite divine mercy, that makes the angels’ sin unforgivable. “There is no repentance for the angels after their fall, just as there is no repentance for men after death” (CCC 393).
As for human beings, Scripture implies that some will not be saved (cf. Matt. 7:13-14), but it has not been given to us to know in this life who has not found salvation. Indeed, in union with God who desires the salvation of all men (cf. 1 Tim. 2:3-4), the Church prays for all who have died and hopes for the salvation of all (cf. CCC 1821).