Jn 3:18
18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
The word condemned here krinó means:
I judge, whether in a law-court or privately: sometimes with cognate nouns emphasizing the notion of the verb, (b) I decide, I think (it) good.
Here in this context the word means :
used specifically of the act of condemning and decreeing (or inflicting) penalty on one !
Its the decreed penalty of God against those ones because of their sins.
Now, who are they that have a penalty of any kind lodged against them by God ?
Its all for whom Christ did not die. You see, all for whom He did die, He took their penalty and condemnation upon Himself, this is so much the Truth that those whom He died for are born into this world as sinners and enemies, already reconciled to God Rom 5:10, already declared righteous Rom 5:19, so it cannot be anyone Christ died for without it being a miscarrying of Divine Justice ! Everyone Christ died for, for them He hath obtained for them Eternal Redemption Heb 9:12
12 Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us.
The word redemption here is the greek word lutrósis and means:
(in the Old Testament: ransoming from imprisonment for debt, or from slavery, release from national misfortune, etc.), liberation, deliverance, release.
the payment of the full ransom-price to free a slave – particularly the redemption of an individual.
Its a having paid a full ransom price,
redemption from the penalty of sin:
So all for whom Christ died, even though they are as other men and women born by nature into the world as filthy sinners, they are nevertheless free from any condemnation from God, and redeemed from any and all penalties due to any and all sin and wrongdoing against God, so much so, that they are born into this World already Reconciled to Him through Christ's Death Rom 5:10 !
So in conclusion, Who are they who are condemned already in Jn 3:18 ? Its simple, anyone for whom Christ did not die !